MRK US Equity☆

Item 1A.Risk Factors.

Summary Risk Factors

The Company is subject to a number of risks that if realized could materially adversely affect its business, results of operations, cash flows, financial condition or prospects. The following is a summary of the principal risk factors facing the Company:

26

Table of Contents

•The Company is dependent on its patent rights, and if its patent rights are invalidated or circumvented, its business could be materially adversely affected.

•As the Company’s products lose market exclusivity, the Company generally experiences a significant and rapid loss of sales from those products.

•Key products generate a significant amount of the Company’s profits and cash flows, and any events that adversely affect the markets for its leading products could have a material adverse effect on the Company’s results of operations, cash flows, financial condition, and prospects.

•The Company’s research and development efforts may not succeed in developing commercially successful products and the Company may not be able to acquire commercially successful products in other ways; consequently, the Company may not be able to replace sales of successful products that lose patent protection.

•The Company’s success is dependent on the successful development and marketing of new products, which are subject to substantial risks.

•The Company faces continued pricing pressure with respect to its products in the public and private sectors.

•Unfavorable or uncertain economic conditions, together with cost-reduction measures being taken by the U.S. and other countries, could negatively affect the Company’s operating results.

•The Company faces intense competition from both lower cost generic and biosimilar products and competitors’ products.

•The Company has significant global operations, which expose it to additional risks, and any adverse event could have a material adverse effect on the Company’s results of operations, cash flows, financial condition, and prospects.

•Climate change or legal, regulatory or market measures to address climate change may negatively affect the Company’s business, results of operations, cash flows, financial condition, and prospects.

•Environmental, social and governance matters may impact the Company’s business and reputation.

•Failure to attract and retain highly qualified personnel could affect the Company’s ability to successfully develop and commercialize products.

•The Company may experience difficulties and delays in manufacturing certain of its products, including vaccines.

•The Company’s business in China experienced significantly lower sales of Gardasil/Gardasil 9 in 2025 and the Company expects that sales of Gardasil/Gardasil 9 in China will not materially increase in 2026. As a consequence of the reduced sales of Gardasil/Gardasil 9, the Company’s business in China declined significantly.

•The Company may not be able to realize the expected benefits of its investments in emerging markets.

•The Company is exposed to market risk from fluctuations in currency exchange rates and interest rates.

•Pharmaceutical products can develop unexpected safety or efficacy concerns.

•Reliance on third-party relationships and outsourcing arrangements could materially adversely affect the Company’s business.

•Negative events in the animal health industry could have a material adverse effect on future results of operations and financial condition of the Company or its Animal Health business.

•Biologics and vaccines carry unique risks and uncertainties, which could have a material adverse effect on the Company’s future results of operations, cash flows, financial condition, and prospects.

•The health care industry in the U.S. has been, and will continue to be, subject to increasing regulation and political action.

•The Company’s products, including products in development, cannot be marketed unless the Company obtains and maintains regulatory approval or authorization.

27

Table of Contents

•Developments following regulatory approval or authorization may adversely affect sales of the Company’s products.

•The Company is subject to a variety of U.S. and international laws and regulations.

•The Company is subject to evolving and complex tax laws, which may result in additional liabilities that may affect results of operations and financial condition.

•Adverse outcomes in current or future legal matters could negatively affect the Company’s business.

•Product liability insurance for products may be limited, cost prohibitive or unavailable.

•The Company is increasingly dependent on sophisticated software applications and computing infrastructure, including the use of cloud-based applications and environments. The Company continues to be a target of cyber-attacks that could lead to a disruption of its worldwide operations, including manufacturing, research and sales operations.

•The Company is increasing its use of artificial intelligence (AI) systems to automate processes, analyze data, and support decision-making, which poses inherent risks.

•Social media and mobile messaging platforms present risks and challenges.

The above list is not exhaustive, and the Company faces additional challenges and risks. Investors should carefully consider all of the information set forth in this Form 10-K, including the following risk factors, before deciding to invest in any of the Company’s securities.

Risk Factors

The risks below are not the only ones the Company faces. Additional risks not currently known to the Company or that the Company presently deems immaterial may also impair its business operations. The Company’s business, financial condition, results of operations, cash flows or prospects could be materially adversely affected by any of these risks. This Form 10-K also contains forward-looking statements that involve risks and uncertainties. The Company’s results could materially differ from those anticipated in these forward-looking statements as a result of certain factors, including the risks it faces described below and elsewhere. See “Cautionary Factors that May Affect Future Results” below.

Risks Related to the Company’s Business

The Company is dependent on its patent rights, and if its patent rights are invalidated or circumvented, its business could be materially adversely affected.

Patent protection is considered, in the aggregate, to be of material importance to the Company’s marketing of human health and animal health products in the U.S. and in most major foreign markets. Patents covering products that it has introduced normally provide market exclusivity, which is important for the successful marketing and sale of its products. The Company seeks patents covering each of its products in each of the markets where it intends to sell the products and where meaningful patent protection is available.

Even if the Company succeeds in obtaining patents covering its products, third parties or government authorities may challenge or seek to invalidate or circumvent its patents and patent applications. It is important for the Company’s business to successfully assert and defend the patent rights that provide market exclusivity for its products. The Company is often involved in patent disputes relating to challenges to its patents or claims by third parties of infringement against the Company. The Company asserts and defends its patents both within and outside the U.S., including by filing claims of infringement against other parties. See Item 8. “Financial Statements and Supplementary Data,” Note 10. “Contingencies and Environmental Liabilities” below. In particular, manufacturers of generic or biosimilar pharmaceutical products from time to time file abbreviated NDAs or BLAs with the FDA seeking to market generic/biosimilar forms of the Company’s products prior to the expiration of relevant patents owned or licensed by the Company. The Company normally responds by asserting one or more of its patents with a lawsuit alleging patent infringement. Patent litigation and other challenges to the Company’s patents are costly and unpredictable and may deprive the Company of market exclusivity for a patented product or, in some cases, third-party patents may prevent the Company from marketing and selling a product in a particular geographic area.

Additionally, certain foreign governments have indicated that compulsory licenses to patents may be granted in the case of national emergencies or in other circumstances, which could diminish or eliminate sales and profits from those regions and negatively affect the Company’s results of operations, cash flows, financial condition, and prospects. Further, court decisions relating to other companies’ patents, potential legislation in both the U.S. and

28

Table of Contents

certain foreign markets relating to patents, as well as regulatory initiatives may result in a more general weakening of intellectual property protection.

If one or more important products lose patent protection in profitable markets, sales of those products are likely to decline significantly as a result of generic or biosimilar versions of those products becoming available. The Company’s business, cash flows, results of operations, financial position, and prospects may be adversely affected by the lost sales unless and until the Company has launched commercially successful products that replace the lost sales. In addition, if products that were measured at fair value and capitalized in connection with acquisitions experience difficulties in the market that negatively affect product cash flows, the Company may recognize material non-cash impairment charges with respect to the value of those products.

A chart listing the key patent protection for certain of the Company’s marketed products, and U.S. patent protection for candidates in Phase 3 clinical development is set forth above in Item 1. “Business — Patents, Trademarks and Licenses.”

As the Company’s products lose market exclusivity, the Company generally experiences a significant and rapid loss of sales from those products.

The Company depends upon patents to provide it with exclusive marketing rights for its products for some period of time. Loss of patent protection for one of the Company’s products typically leads to a significant and rapid loss of sales for that product as lower priced generic or biosimilar versions become available. In the case of products that contribute significantly to the Company’s sales, the loss of market exclusivity can have a material adverse effect on the Company’s business, cash flows, results of operations, financial condition and prospects. Bridion will lose market exclusivity in the U.S. in July 2026 at which time the Company anticipates a significant and rapid decline in U.S. sales of Bridion. The Company expects to discontinue U.S. sales of Bridion by the end of 2026. In addition, Januvia and Janumet will lose market exclusivity in the U.S. in May 2026 and Janumet XR will lose market exclusivity in the U.S. in July 2026. The Company expects a significant decline in sales of Januvia in the first half of 2026 reflecting the impact of government price setting noted above and subsequently, following loss of market exclusivity in May 2026, the Company anticipates it will lose nearly all U.S. sales of Januvia and Janumet. Also, the Company expects that sales of Keytruda will be materially negatively impacted by biosimilar competition between 2028 and 2029. As previously disclosed, while two patents in the Keytruda composition of matter patent family expire in May and November of 2029, respectively, the Company expects these patents to be the subject of litigation and, thus, biosimilar competition could begin in December 2028 when the primary compound patent expires. The Company also expects to lose market exclusivity in Europe for Keytruda in 2031 following compound patent expiration. There may, however, be attempts by one or more companies to challenge the patent or launch a biosimilar product despite the patent in some European jurisdictions following the expiration of data exclusivity in Europe in July 2026.

Key products generate a significant amount of the Company’s profits and cash flows, and any events that adversely affect the markets for its leading products could have a material adverse effect on the Company’s results of operations, cash flows, financial condition, and prospects.

The Company’s ability to generate profits and operating cash flows depends largely upon the continued profitability of the Company’s key products, such as Keytruda, Gardasil/Gardasil 9, Lynparza, Winrevair, and Bravecto. In particular, in the aggregate, in 2025, sales of Keytruda represented 49% of the Company’s total sales. As a result of the Company’s dependence on key products, any event that adversely affects any of these products or the markets for any of these products, such as the materially lower demand for Gardasil/Gardasil 9 in China which the Company has experienced, could have a significant adverse impact on results of operations, cash flows, financial condition, and prospects. Other events could include loss of patent protection, selection for IRA price setting, lower than expected utilization of Keytruda Qlex, increased costs associated with manufacturing, generic, biosimilar or over-the-counter availability of the Company’s product or a competitive product, the discovery of previously unknown side effects, results of post-approval trials, increased competition from the introduction of new, more effective treatments and discontinuation or removal from the market of the product for any reason. Such events could have a material adverse effect on the sales of any such products.

The Company’s research and development efforts may not succeed in developing commercially successful products and the Company may not be able to acquire commercially successful products in other ways; consequently, the Company may not be able to replace sales of successful products that lose patent protection.

In order to remain competitive, the Company, like other major pharmaceutical companies, must continue to launch new products. Expected declines in sales of products after the loss of market exclusivity mean that the Company’s future success is dependent on its pipeline of new products, including new products that it may develop

29

Table of Contents

through collaborations and joint ventures and products that it is able to obtain through license or acquisition. To accomplish this, the Company commits substantial effort, funds and other resources to research and development, both through its own dedicated resources and through various collaborations with third parties. There is a high rate of failure inherent in the research and development process for new drugs and vaccines. As a result, there is a high risk that funds invested by the Company in research programs will not generate financial returns. This risk profile is compounded by the fact that this research has a long investment cycle. To bring a pharmaceutical compound from the discovery phase to market may take a decade or more and failure can occur at any point in the process, including later in the process after significant funds have been invested.

For a description of the research and development process, see Item 1. “Business — Research and Development” above. Each phase of testing is highly regulated and during each phase there is a substantial risk that the Company will encounter serious obstacles or will not achieve its goals. Therefore, the Company may abandon a product candidate or use in which it has invested substantial amounts of time and resources. Some of the risks encountered in the research and development process include the following: preclinical testing of a new compound may yield disappointing results; competing products from other manufacturers may reach the market first; clinical trials of a new drug may not be successful; a new drug may not be effective or may have harmful side effects; a new drug may not be approved by the regulators for its intended use; it may not be possible to obtain a patent for a new drug; payers may refuse to cover or reimburse the new product; or sales of a new product may be disappointing.

The Company cannot state with certainty when or whether any of its products now under development will be approved or launched; whether it will be able to develop, license or otherwise acquire compounds, product candidates or products; or whether any products, once launched, will be commercially successful. The Company must maintain a continuous flow of successful new products and successful new indications for existing products sufficient both to cover its substantial research and development costs and to replace sales that are lost as profitable products lose market exclusivity or are displaced by competing products or therapies. Failure to do so in the short term or long term would have a material adverse effect on the Company’s business, results of operations, cash flows, financial condition and prospects.

The Company’s success is dependent on the successful development and marketing of new products, which are subject to substantial risks.

Product candidates or uses that appear promising in development may fail to reach the market or fail to succeed for numerous reasons, including the following:

•findings of ineffectiveness, superior safety or efficacy of competing products, or harmful side effects in clinical or preclinical testing;

•failure to receive the necessary regulatory approvals, including delays in the approval of new products and new indications, or the anticipated labeling, and uncertainties about the time required to obtain regulatory approvals and the benefit/risk standards applied by regulatory agencies in determining whether to grant approvals;

•failure in certain markets to obtain reimbursement commensurate with the level of innovation and clinical benefit presented by the product;

•changes in clinical preferences or standards of care, including competitor innovations, that diminish the value of the product;

•lack of economic feasibility due to manufacturing costs or other factors; and

•preclusion from commercialization by the proprietary rights of others.

In the future, if certain pipeline programs are cancelled or if the Company believes that their commercial prospects have been reduced, the Company may recognize material non-cash impairment charges for those programs that were measured at fair value and capitalized in connection with acquisitions or certain collaborations.

Failure to successfully develop and market new products in the short term or long term would have a material adverse effect on the Company’s business, results of operations, cash flows, financial condition and prospects.

The Company faces continued pricing pressure with respect to its products in the public and private sectors.

The Company faces continued pricing pressure globally and, particularly in mature markets, from managed care organizations, government agencies and programs that could negatively affect the Company’s sales

30

Table of Contents

and profit margins. In the U.S., these include (i) U.S. federal laws and regulations related to Medicare and Medicaid, including the Medicare Prescription Drug Improvement and Modernization Act of 2003, the ACA, and the IRA, (ii) practices of managed care groups and institutional and governmental purchasers, and (iii) state activities aimed at increasing price transparency, including new laws as noted above in Item 1. “Competition and the Health Care Environment.” Changes to the health care system enacted as part of health care reform in the U.S., as well as increased purchasing power of entities that negotiate on behalf of Medicare, Medicaid, and private sector beneficiaries, could result in further pricing pressures. As noted in Item 1. “Competition and the Health Care Environment,” in 2023, HHS selected Januvia for the first year of the IRA’s price setting program, which resulted in a government set price becoming effective on January 1, 2026. In 2025, HHS selected Janumet and Janumet XR for government price setting, which will become effective on January 1, 2027. In addition, in January 2026, HHS announced that Lenvima has been selected for government price setting, the set price for which will become effective on January 1, 2028. Furthermore, the Company expects that in 2027 HHS will include Keytruda in a subsequent selection of products to undergo IRA price setting, with such price to become effective on January 1, 2029 and the Company expects that, as a result, U.S. sales of Keytruda will decline materially after that time. Government price setting may also impact pricing in the private market, negatively affecting the Company’s performance.

Also, as noted above, in December 2025, the Company entered into the MFN Agreement with the U.S. government pursuant to which the Company will provide key products through a direct-to-patient program at affordable prices for eligible patients in the U.S. This currently includes Januvia, Janumet, and Janumet XR, and will be expanded in the future to include enlicitide decanoate pending FDA approval. The Company also agreed to offer its existing medicines at discounted prices to Medicaid, excluding certain products. In addition, the Company has agreed that products launched during the term of the MFN Agreement (with certain exceptions) will be subject to “most-favored-nation” pricing in reference to prices for such products in the MFN Countries.

In addition, in the U.S., larger customers have received higher rebates on drugs in certain highly competitive categories. The Company must also compete to be placed on formularies of managed care organizations. Exclusion of a product from a formulary can lead to reduced usage in the managed care organization. The Company is also facing pricing pressure from purchasers of certain vaccines in highly competitive categories. Also, the Company expects that U.S. states will continue their focus on pharmaceutical pricing and may shift to more aggressive price control tools.

Outside the U.S., numerous major markets, including the EU, Japan and China have pervasive government involvement in funding health care and, in that regard, fix the pricing and reimbursement of pharmaceutical and vaccine products. Consequently, in those markets, the Company is subject to government decision making and budgetary actions with respect to its products. In Japan, the pharmaceutical industry is subject to government-mandated annual price reductions of pharmaceutical products and certain vaccines. Furthermore, the Japanese government can order re-pricing for specific products if it determines that use of such product will exceed certain thresholds defined under applicable re-pricing rules.

The Company expects pricing pressures to continue in the future.

Unfavorable or uncertain economic conditions, together with cost-reduction measures being taken by the U.S. and other countries, could negatively affect the Company’s operating results.

The Company’s business may be adversely affected by local and global economic conditions, including with respect to inflation, interest rates, and costs of raw materials and packaging. Uncertainty in global economic and geopolitical conditions may result in a slowdown to the global economy that could affect the Company’s business by reducing the prices that drug wholesalers and retailers, hospitals, government agencies and managed health care providers may be able or willing to pay for the Company’s products or by reducing the demand for the Company’s products, which could in turn negatively impact the Company’s sales and result in a material adverse effect on the Company’s business, cash flows, results of operations, financial condition and prospects.

As discussed above in Item 1. “Competition and the Health Care Environment,” global efforts toward health care cost containment continue to exert pressure on product pricing and market access worldwide. Changes to the U.S. health care system as part of health care reform, as well as increased purchasing power of entities that negotiate on behalf of Medicare, Medicaid, and private sector beneficiaries, have contributed to pricing pressure. In several international markets, government-mandated pricing actions have reduced prices of generic and patented drugs. In addition, the Company’s sales performance in 2025 was negatively affected by other cost-reduction measures taken by governments and other third parties to lower health care costs, including in the U.S., the expansion of the Federal 340B Drug Discount Program. The Company anticipates all of these actions, and additional actions in the future, will continue to negatively affect sales and profits.

31

Table of Contents

In addition, it is possible that as a consequence of the MFN Agreement, certain of the Company’s products may not be launched in the MFN Countries or their launch may be delayed and as a result, the MFN Countries may take actions that adversely impact the Company.

If credit and economic conditions worsen, the resulting economic and currency impacts in the affected markets and globally could have a material adverse effect on the Company’s results.

The Company faces intense competition from both lower cost generic and biosimilar products and competitors’ products.

In general, the Company faces increasing competition from lower-cost generic and biosimilar products. The patent rights that protect its products are of varying strengths and durations. In addition, in some countries, patent protection is significantly weaker than in the U.S. or in the EU. In the U.S. and the EU, political pressure to reduce spending on prescription drugs has led to legislation and other measures that encourage the use of generic and biosimilar products. Although it is the Company’s policy to actively protect its patent rights, challenges to the Company’s products can arise at any time, and the Company’s patents may not prevent the emergence of generic or biosimilar competition for its products.

Loss of patent protection for a product typically is followed promptly by generic or biosimilar substitutes, reducing the Company’s sales of that product. Availability of generic or biosimilar substitutes for the Company’s drugs may adversely affect its results of operations and cash flows. In addition, proposals emerge from time to time in the U.S. and other countries for legislation to further encourage the early and rapid approval of generic or biosimilar drugs. Any such proposal that is enacted into law could worsen this substantial negative effect on the Company’s business, cash flows, results of operations, financial condition and prospects.

Also, the Company’s products face intense competition from competitors’ products. This competition may increase as new products enter the market. In such an event, the competitors’ products may be safer or more effective, more convenient to use, have better insurance coverage or reimbursement levels or be more effectively marketed and sold than the Company’s products. Alternatively, in the case of generic or biosimilar competition, including the generic or biosimilar availability of competitors’ branded products, they may be equally safe and effective products that are sold at a substantially lower price than the Company’s products. As a result, if the Company fails to maintain its competitive position, this could have a material adverse effect on its business, cash flows, results of operations, financial condition and prospects. In addition, if products that were measured at fair value and capitalized in connection with acquisitions experience difficulties in the market that negatively impact product cash flows, the Company may recognize material non-cash impairment charges with respect to the value of those products.

The Company has significant global operations, which expose it to additional risks, and any adverse event could have a material adverse effect on the Company’s results of operations, cash flows, financial condition, and prospects.

The extent of the Company’s operations outside the U.S. is significant. Risks inherent in conducting a global business include:

•changes in medical reimbursement policies and programs and pricing restrictions in key markets;

•multiple regulatory requirements that could restrict the Company’s ability to manufacture and sell its products in key markets;

•trade protection measures and import or export licensing requirements, including the imposition of trade sanctions or similar restrictions by the U.S. or other governments;

•the imposition of tariffs by the U.S. or other governments;

•foreign exchange fluctuations;

•diminished protection of intellectual property in some countries; and

•possible nationalization and expropriation.

In addition, there may be changes to the Company’s business if there is instability, disruption or destruction in a significant geographic region, regardless of cause, including war, terrorism, riot, civil insurrection or social unrest; and natural or man-made disasters, including famine, flood, fire, earthquake, storm or disease. Events like these, such as the ongoing war between Russia and Ukraine, and conflict in the Middle East, and/or policy changes with respect to international trade protection measures, could result in material adverse effects on

32

Table of Contents

macroeconomic conditions, currency exchange rates and financial markets, and may adversely affect the Company’s business, results of operations, cash flows, financial condition, and prospects.

Climate change or legal, regulatory or market measures to address climate change may negatively affect the Company’s business, results of operations, cash flows, financial condition, and prospects.

The Company believes that climate change has the potential to negatively affect its business, results of operations, cash flows and prospects. The Company is exposed to physical risks (such as extreme weather conditions, inland flooding or rising sea levels), risks in transitioning to a low-carbon economy (such as additional legal or regulatory requirements, changes in technology, market risk and reputational risk) and social and human effects (such as population dislocations and harm to health and well-being) associated with climate change. These risks can be either acute (short-term) or chronic (long-term).

The adverse impacts of climate change include increased frequency and severity of natural disasters and extreme weather events such as hurricanes, tornados, wildfires (exacerbated by drought), flooding, and extreme heat. Extreme weather, inland flooding and sea-level rise pose physical risks to the Company’s facilities as well as those of its suppliers. Such risks include losses incurred as a result of physical damage to facilities, loss or spoilage of inventory, and business interruption caused by such natural disasters and extreme weather events. Other potential physical impacts due to climate change include reduced access to high-quality water in certain regions and the loss of biodiversity, which could impact future product development. These risks could disrupt the Company’s operations and its supply chain, which may result in increased costs.

New legal and regulatory requirements with respect to climate-related matters, which may differ across jurisdictions, could result in the Company being subject to increased compliance burdens and costs to meet these obligations. The Company’s supply chain would likely be subject to similar risks and would likely pass along any increased costs to the Company, which may affect the Company’s ability to procure raw materials or other supplies required for the operation of the Company’s business at the quantities and levels required.

Environmental, social and governance matters may impact the Company’s business and reputation.

Governmental authorities, non-governmental organizations, customers, investors, external stakeholders and employees are sensitive to environmental, social and governance concerns, such as human capital, climate change, water use, recyclability or recoverability of packaging, and plastic waste. The focus on these concerns may lead to new requirements that could result in increased costs associated with developing, manufacturing and distributing the Company’s products, and related reporting obligations. The Company’s ability to compete could also be affected by changing customer preferences and requirements, such as growing demand for validated net zero GHG emission targets and more environmentally friendly products, packaging or supplier practices, or by failure to meet such customer expectations or demand. The Company risks negative shareholder reaction, including from proxy advisory services, as well as damage to its brand and reputation and inability to attract and retain employee talent, if the Company fails to act responsibly, or if the Company is perceived to not be acting responsibly, in key areas, including equitable access to medicines and vaccines, product quality and safety, environmental stewardship, reduction of GHG emissions, support for local communities, corporate governance and transparency, and addressing human capital factors in the Company’s operations. Responding to these considerations as well as any applicable regulatory requirements and implementation of the Company’s goals and initiatives involves risks and uncertainties, requires investments, and depends in part on third-party performance or data that is outside of the Company’s control. In addition, some governmental authorities, non-governmental organizations, and stakeholders may disagree with the Company’s goals and initiatives. If the Company does not meet the rapidly evolving and varied regulatory requirements and expectations of its investors, customers and other stakeholders, the Company could experience negative impacts to the Company’s business and results of operations. In addition, the Company is subject to evolving mandatory and voluntary reporting, diligence and disclosure requirements, including the EU’s Corporate Sustainability Reporting Directive (CSRD) and potentially the SEC’s climate-related reporting requirements (which are currently stayed), the legislation in California requiring reporting of GHG emissions (which is currently subject to legal challenge) and climate risk (which is currently stayed pending appeal), and similar regulatory requirements in other jurisdictions outside the U.S. These evolving regulatory requirements may result in increased costs and complexities of compliance in order to collect, measure and report on the relevant information, and could expose the Company to the risk of government enforcement actions and private litigation.

33

Table of Contents

Failure to attract and retain highly qualified personnel could affect the Company’s ability to successfully develop and commercialize products.

The Company’s success is largely dependent on its continued ability to attract and retain highly qualified scientific, technical and management personnel, as well as personnel with expertise in clinical research and development, governmental regulation and commercialization. Competition for qualified personnel in the pharmaceutical industry, both in the U.S. and internationally, is intense. The Company cannot be certain that it will be able to attract and retain qualified personnel or that the costs of doing so will not materially increase.

The Company may experience difficulties and delays in manufacturing certain of its products, including vaccines.

Merck from time to time experiences difficulties in manufacturing certain of its products, including vaccines. The Company may, in the future, experience other difficulties and delays in manufacturing its products, such as (i) failure of the Company or any of its vendors or suppliers to comply with Current Good Manufacturing Practices and other applicable regulations and quality assurance guidelines that could lead to manufacturing shutdowns, product shortages and delays in product manufacturing; (ii) delays related to the construction of new facilities or the expansion of existing facilities, including those intended to support future demand for the Company’s products; and (iii) other manufacturing or distribution problems including supply chain delays, shortages in raw materials, changes in manufacturing production sites and limits to manufacturing capacity due to regulatory requirements, changes in types of products produced, or physical limitations that could impact continuous supply. In addition, the Company could experience difficulties or delays in manufacturing its products caused by natural disasters, such as hurricanes. Manufacturing difficulties can result in product shortages, leading to lost sales and reputational harm to the Company.

The Company’s business in China experienced significantly lower sales of Gardasil/Gardasil 9 in 2025 and the Company expects that sales of Gardasil/Gardasil 9 in China will not materially increase in 2026. As a consequence of the reduced sales of Gardasil/Gardasil 9, the Company’s business in China declined significantly.

The Company’s business in China experienced significantly lower sales of Gardasil/Gardasil 9 in 2025. Due to above normal inventory levels at the Company’s commercialization partner in China, the Company made a decision to pause shipments to China beginning in February 2025 and has not resumed shipments to date. The Company will not resume shipments until inventory levels return to normal levels and it cannot predict when shipments to China will resume nor the levels of sales that the Company will achieve and as a result, the Company expects that sales of Gardasil/Gardasil 9 in China will not materially increase in 2026. In June 2025, a nine-valent HPV vaccine produced by a local manufacturer received regulatory approval in China for use in females 9-45 years of age.

Furthermore, the government's anti-corruption campaign, particularly the increased number of inspections and audits, could substantially increase the administrative burden on health care institutions and health care professionals throughout the whole industry in China and potentially have a negative impact on the Company's sales. In addition to its commercial operations, the Company has significant research and manufacturing operations in China, including working with Chinese entities such as Wuxi Apptech Co., Ltd. If geopolitical tensions were to increase and disrupt the Company’s operations in China, such disruption could result in a material adverse effect on the Company’s product development, sales, business, cash flows, results of operations, financial condition and prospects.

Also, growth of the Company’s business in China is dependent upon ongoing development of a favorable environment for innovative pharmaceutical products and vaccines, sustained access for the Company’s currently marketed products, and the absence of trade impediments or adverse pricing controls. As noted above in Item 1. “Competition and the Health Care Environment,” pricing pressure in China has increased as the Chinese government has been taking steps to reduce costs, including implementing health care reform that has led to the acceleration of generic substitution, where available. While the mechanism for drugs being added to the NRDL evolves, inclusion may require a price negotiation which could impact the outlook in the market for selected brands. A new NRDL was recently completed in which new entries averaged approximately 60% price reductions. While pricing pressure has always existed in China, health care reform has increased this pressure in part due to the acceleration of generic substitution through the government’s VBP program. The government has implemented the VBP program through a tendering process for mature products which have generic substitutes with a Generic Quality Consistency Evaluation approval. Mature products that have entered into the latest rounds of VBP had, on average, a price reduction of more than 50%. The Company expects that the VBP process will have a significant impact on mature products moving forward.

34

Table of Contents

The Company may not be able to realize the expected benefits of its investments in emerging markets.

The Company has been taking steps to increase its sales in emerging markets. However, there is no guarantee that the Company’s efforts to expand sales in these markets will succeed. Some countries within emerging markets may be especially vulnerable to periods of global financial instability or may have very limited resources to spend on health care. In order for the Company to operate successfully in emerging markets, it must attract and retain qualified personnel. The Company may also be required to increase its reliance on third-party agents within less developed markets, which may affect its ability to realize continued growth and may also increase the Company’s risk exposure. In addition, many of these countries have currencies that fluctuate substantially and, if such currencies devalue and the Company cannot offset the devaluations, the Company’s financial performance within such countries could be adversely affected.

For all these reasons, sales within emerging markets carry significant risks. However, at the same time, macro-economic growth of selected emerging markets is expected to lead to significant increased health care spending in those countries and access to innovative medicines for patients. A failure to maintain the Company’s presence in emerging markets could therefore have a material adverse effect on the Company’s business, cash flows, results of operations, financial condition and prospects.

The Company is exposed to market risk from fluctuations in currency exchange rates and interest rates.

The Company operates in multiple jurisdictions and virtually all sales are denominated in currencies of the local jurisdiction. Additionally, the Company has entered and will enter into business development transactions, borrowings or other financial transactions that may give rise to currency and interest rate exposure.

Since the Company cannot, with certainty, foresee and mitigate against such adverse changes, fluctuations in currency exchange rates, interest rates and inflation could negatively affect the Company’s business, cash flows, results of operations, financial condition and prospects. For example, Argentina is currently experiencing hyperinflation, which is affecting the Company’s operations in that market.

In order to mitigate against the adverse impact of these market fluctuations, the Company will from time to time enter into hedging agreements. While hedging agreements, such as currency options and forwards, and interest rate swaps, may limit some of the exposure to exchange rate and interest rate fluctuations, such attempts to mitigate these risks may be costly and not always successful.

Pharmaceutical products can develop unexpected safety or efficacy concerns.

Unexpected safety or efficacy concerns can arise with respect to marketed products, whether or not scientifically justified, leading to product recalls, withdrawals, or declining sales, as well as product liability, consumer fraud and/or other claims, including potential civil or criminal governmental actions.

Reliance on third-party relationships and outsourcing arrangements could materially adversely affect the Company’s business.

The Company depends on third parties, including suppliers, distributors, alliances with other pharmaceutical and biotechnology companies, and third-party service providers, for key aspects of its business including development, manufacture and commercialization of its products and support for its information technology (IT) systems. Failure of these third parties to meet their contractual, regulatory and other obligations to the Company or the development of factors that materially disrupt the relationships between the Company and these third parties could have a material adverse effect on the Company’s business.

Negative events in the animal health industry could have a material adverse effect on future results of operations and financial condition of the Company or its Animal Health business.

Future sales of key animal health products could be adversely affected by a number of risk factors including certain risks that are specific to the animal health business. For example, the outbreak of disease carried by animals, such as Avian Influenza or African Swine Fever, could lead to their widespread death and precautionary destruction as well as the reduced consumption and demand for animals, which could adversely affect the Company’s results of operations. Also, the outbreak of any highly contagious diseases near the Company’s main production sites could require the Company to immediately halt the manufacture of its animal health products at such sites or force the Company to incur substantial expenses in procuring raw materials or products elsewhere. Other risks specific to animal health include epidemics and pandemics affecting livestock, government procurement and pricing practices, weather and global agribusiness economic events. In addition, in 2025, sales of the Bravecto family of products were

35

Table of Contents

$1.1 billion, which represented 18% of the Company’s Animal Health segment sales. Any negative event with respect to the Bravecto family of products could have a material adverse effect on the Company’s Animal Health sales. If the Animal Health segment of the Company’s business becomes more significant, the impact of any such events on future results of operations could also become more significant.

Biologics and vaccines carry unique risks and uncertainties, which could have a material adverse effect on the Company’s future results of operations, cash flows, financial condition, and prospects.

The successful development, testing, manufacturing and commercialization of biologics and vaccines, particularly human and animal health vaccines, is a long, complex, expensive and uncertain process. There are unique risks and uncertainties related to biologics and vaccines, including:

•There may be limited access to, and supply of, normal and diseased tissue samples, cell lines, pathogens, bacteria, viral strains and other biological materials. In addition, government regulations in multiple jurisdictions, such as the U.S. and the EU, could result in restricted access to, or transport or use of, such materials. If the Company loses access to sufficient sources of such materials, or if tighter restrictions are imposed on the use of such materials, the Company may not be able to conduct research activities as planned and may incur additional development costs.

•The development, manufacturing and marketing of biologics and vaccines are subject to regulation by the FDA, the EMA and other regulatory bodies. These regulations are often more complex and extensive than the regulations applicable to other pharmaceutical products. For example, in the U.S., a BLA, including both preclinical and clinical trial data and extensive data regarding manufacturing procedures, is required for human vaccine candidates, and FDA approval is generally required for the release of each manufactured commercial human vaccine lot.

•Manufacturing biologics and vaccines, especially in large quantities, is complex and may require the use of innovative technologies to handle living micro-organisms. Each lot of an approved biologic and vaccine must undergo thorough testing for identity, strength, quality, purity and potency. Manufacturing biologics requires facilities specifically designed for and validated for this purpose, and sophisticated quality assurance and quality control procedures are necessary. Slight deviations anywhere in the manufacturing process, including filling, labeling, packaging, storage and shipping, and quality control and testing, may result in lot failures, product recalls or spoilage. When changes are made to the manufacturing process, the Company may be required to provide preclinical and clinical data showing the comparable identity, strength, quality, purity or potency of the biologics and vaccines before and after such changes.

•Biologics and vaccines are costly to manufacture because production ingredients are derived from living animal or plant material, and most biologics and vaccines cannot be made synthetically. In particular, keeping up with the demand for vaccines may be difficult due to the complexity of producing vaccines.

•The use of biologically derived ingredients can lead to variability in the manufacturing process and could lead to allegations of harm, including infections or allergic reactions, which allegations would be reviewed through a standard investigation process that could lead to closure of product facilities due to possible contamination. Any of these events could result in substantial costs.

•Biologics and vaccines require long manufacturing lead times, sometimes requiring planning years in advance of demand, which could increase the risk of inventory write-downs if that demand does not materialize.

Risks Relating to Government Regulation and Legal Proceedings

The health care industry in the U.S. has been, and will continue to be, subject to increasing regulation and political action.

As discussed above in Item 1. “Competition and the Health Care Environment,” the Company believes that the health care industry will continue to be subject to increasing regulation as well as political and legal action, as future proposals to reform the health care system are considered by the Executive Branch, Congress and state legislatures.

In 2022, Congress passed the IRA, which made significant changes to how drugs are covered and paid for under the Medicare program, including the creation of financial penalties for drugs whose prices rise faster than the rate of inflation, redesign of the Medicare Part D program to require manufacturers to bear more of the liability for certain drug benefits, which has taken effect in 2025, and government price setting for certain Medicare Part D drugs,

36

Table of Contents

starting in 2026, and Medicare Part B drugs starting in 2028. Furthermore, government price setting may also impact pricing in the private market, negatively affecting the Company’s performance. As noted in Item 1. “Competition and the Health Care Environment,” in 2023, HHS selected Januvia for the first year of the IRA’s price setting program, which resulted in a government set price becoming effective on January 1, 2026. In 2025, HHS selected Janumet and Janumet XR for government price setting, the set price for which will become effective on January 1, 2027. In addition, in January 2026, HHS announced that Lenvima has been selected for government price setting, the set price for which will become effective on January 1, 2028. Furthermore, the Company expects that in 2027 HHS will include Keytruda in a subsequent selection of products to undergo IRA price setting, with such price to become effective on January 1, 2029 and the Company expects that, as a result, U.S. sales of Keytruda will decline materially after that time.

In addition, in 2021, Congress passed the American Rescue Plan Act, which included a provision that eliminated the statutory cap on rebates drug manufacturers pay to Medicaid. These rebates act as a discount off the list price and eliminating the cap means that manufacturer discounts paid to Medicaid can increase. Prior to this change, manufacturers have not been required to pay more than 100% of the Average Manufacturer Price (AMP) in rebates to state Medicaid programs for Medicaid-covered drugs. As a result of this provision, manufacturers may have to pay state Medicaid programs more in rebates than they received on sales of particular products. This change presents a risk to Merck for drugs that have high Medicaid utilization and rebate exposure that is more than 100% of the AMP. Additionally, increased utilization of the 340B Federal Drug Discount Program and restrictions on the Company’s ability to identify inappropriate discounts are having a negative impact on the Company’s performance. Also, the Company expects that states will continue their focus on pharmaceutical pricing and will increasingly shift to more aggressive price control tools such as Prescription Drug Affordability Boards that have the authority to conduct affordability reviews and establish upper payment limits and that Company products may be selected for such reviews.

In the U.S., members of the government have made public statements in favor of, and may take steps to implement, various regulatory or policy changes that could negatively impact the pharmaceutical industry, including the Company. Those potential changes include some related to vaccines and vaccine development, as well as personnel and policy changes at the FDA and other government agencies, committees, and programs. For example, HHS could undergo changes that could make it more difficult for the FDA to grant regulatory approvals for drugs and vaccines. Additionally, if the FDA drug user fee programs were eliminated, that could cause significant delays to facility inspections and approvals of new products. Changes could also impact the CDC, including how recommendations for immunizations are issued and maintained. Changes that have been made to the CDC’s recommended immunization schedule which could impact public and private coverage, as well as reduction in state-controlled school immunization requirements, could cause a decline in vaccine uptake. Alterations to the National Vaccine Injury Compensation Program also could impact how claims against vaccine manufacturers are adjudicated. The government also has discussed certain policy changes to facilitate market entry of biosimilar products. It is too early for the Company to assess which, if any, of the regulatory or policy changes that have been publicly referenced would be implemented or how they would impact the market, and the Company cannot predict what additional future changes in the health care industry in general, or the pharmaceutical industry in particular, will occur; however, any changes could have a material adverse effect on the Company’s business, cash flows, results of operations, financial condition and prospects.

The Company’s products, including products in development, cannot be marketed unless the Company obtains and maintains regulatory approval or authorization.

The Company’s activities, including research, preclinical testing, clinical trials and the manufacturing and marketing of its products, are subject to extensive regulation by numerous federal, state and local governmental authorities in the U.S., including the FDA, and by foreign regulatory authorities, including in the EU, Japan and China. In the U.S., the FDA administers requirements covering the testing, approval, safety, effectiveness, manufacturing, labeling and marketing of prescription pharmaceuticals and vaccines. In some cases, the FDA requirements have increased the amount of time and resources necessary to develop new products and bring them to market in the U.S. Regulation outside the U.S. also is primarily focused on drug safety and effectiveness and, in many cases, reduction in the cost of drugs. The FDA and foreign regulatory authorities, including in the EU, Japan and China, have substantial discretion to require additional testing, to delay or withhold registration and marketing approval and to otherwise preclude distribution and sale of a product.

Even if the Company is successful in developing new products, it will not be able to market any of those products unless and until it has obtained all required regulatory approvals (which in limited circumstances may include authorizations for emergency use) in each jurisdiction where it proposes to market the new products. Once obtained, the Company must maintain approval as long as it plans to market its new products in each jurisdiction where approval is required. The Company’s failure to obtain approval, significant delays in the approval process, or its

37

Table of Contents

failure to maintain approval in any jurisdiction will prevent it from selling the products in that jurisdiction and realizing sales.

Developments following regulatory approval or authorization may adversely affect sales of the Company’s products.

Even after a product reaches the market, certain developments following regulatory approval may decrease demand for the Company’s products, including the following:

•results in post-approval Phase 4 trials or other studies;

•the re-review of products or indications that are already marketed;

•the recall or loss of marketing approval of products that are already marketed;

•changing government standards or public expectations regarding safety, efficacy, quality or labeling changes;

•scrutiny of advertising and promotion; and

•the withdrawal of indications granted pursuant to accelerated approvals.

In the past, clinical trials and post-marketing surveillance of certain marketed drugs of the Company and of competitors within the industry have raised concerns that have led to recalls, withdrawals or adverse labeling of marketed products. Clinical trials and post-marketing surveillance of certain marketed drugs also have raised concerns among some prescribers and patients relating to the safety or efficacy of pharmaceutical products in general that have negatively affected the sales of such products. In addition, increased scrutiny of the outcomes of clinical trials has led to increased volatility in market reaction. Further, these matters often attract litigation and, even where the basis for the litigation is groundless, considerable resources may be needed to respond.

In addition, following in the wake of product withdrawals and other significant safety issues, health authorities such as the FDA, the EMA, Japan’s PMDA and China’s NMPA have increased their focus on safety when assessing the benefit/risk balance of drugs. Some health authorities appear to have become more cautious when making decisions about approvability of new products or indications.

If previously unknown side effects are discovered or if there is an increase in negative publicity regarding known side effects of any of the Company’s products, it could significantly reduce demand for the product or require the Company to take actions that could negatively affect sales, including removing the product from the market, restricting its distribution or applying for labeling changes. Similarly, new information that becomes available about products from other manufacturers may prompt new regulatory reviews of the Company’s products, leading to actions that could negatively affect sales. Further, in the environment in which all pharmaceutical companies operate, the Company is at risk for product liability and consumer protection claims and civil and criminal governmental actions related to its products, research and/or marketing activities. In addition, dissemination of promotional materials through evolving digital channels serves to increase visibility and scrutiny in the marketplace.

The Company is subject to a variety of U.S. and international laws and regulations.

The Company is currently subject to a number of government laws and regulations and, in the future, could become subject to new government laws and regulations. The costs of compliance with such laws and regulations, or the negative results of non-compliance, could adversely affect the business, cash flows, results of operations, financial condition and prospects of the Company; these laws and regulations include (i) additional health care reform initiatives in the U.S. or in other countries, including additional mandatory discounts or fees; (ii) the U.S. Foreign Corrupt Practices Act (FCPA) or other anti-bribery and corruption laws; (iii) new laws, regulations and judicial or other governmental decisions affecting pricing, drug reimbursement, and access or marketing within or across jurisdictions; (iv) changes in intellectual property laws; (v) changes in accounting standards; (vi) new and increasing data privacy regulations and enforcement, particularly in the EU, the U.S., and China; (vii) legislative mandates or preferences for local manufacturing of pharmaceutical or vaccine products; (viii) emerging and new global regulatory requirements for reporting payments and other value transfers to health care professionals; (ix) sustainability regulations, such as the EU’s CSRD; and (x) the potential impact of importation restrictions, embargoes, trade sanctions and legislative and/or other regulatory changes.

The Company is subject to evolving and complex tax laws, which may result in additional liabilities that may affect results of operations and financial condition.

The Company is subject to evolving and complex tax laws in the jurisdictions in which it operates. Significant judgment is required for determining the Company’s tax liabilities, and the Company’s tax returns are

38

Table of Contents

routinely examined by various tax authorities. The Internal Revenue Service (IRS) is currently conducting examinations of the Company’s tax returns for the years 2017 and 2018, including the one-time transition tax enacted under the Tax Cuts and Jobs Act of 2017 (TCJA). If the IRS’ challenge to the Company’s transition tax position is ultimately successful, the impact could be material to the Company’s cash flows, results of operations and financial condition. The IRS is also currently conducting examinations of the Company’s tax returns for the years 2021 and 2022. In addition, various state and foreign tax examinations are in progress. In connection with the Organization for Economic Cooperation and Development (OECD) Base Erosion and Profit Shifting project, companies are required to disclose more information to tax authorities on operations around the world, which may lead to greater audit scrutiny of profits earned in other countries. The Company believes that its accrual for tax contingencies is adequate for all open years based on past experience, interpretations of tax law, and judgments about potential actions by tax authorities; however, due to the complexity of tax contingencies, the ultimate resolution of any tax matters may result in payments greater or less than amounts accrued. In addition, the Company may be negatively affected by changes in tax laws, or new tax laws, affecting, for example, tax rates, and/or revised tax law interpretations in domestic or foreign jurisdictions, including, among others, any potential changes to the existing U.S. tax law by the Executive Branch and Congress, as well as any changes in tax law resulting from the implementation of the OECD’s two-pillar solution to reform the international tax landscape.

The Company has taken the position, based on the opinions of tax counsel, that its distribution of Organon & Co. (Organon) common stock in connection with the 2021 spin-off (Spin-Off) qualifies as a transaction that is tax-free for U.S. federal income tax purposes. If any facts, assumptions, representations, and undertakings from the Company and Organon regarding the past and future conduct of their respective businesses and other matters are incorrect or not otherwise satisfied, the Spin-Off may not qualify for tax-free treatment, which could result in significant U.S. federal income tax liabilities for the Company and its shareholders.

Adverse outcomes in current or future legal matters could negatively affect the Company’s business.

Current or future litigation, claims, proceedings and government investigations could preclude or delay the commercialization of the Company’s products or could adversely affect the Company’s business, results of operations, cash flows, financial condition and prospects. Such legal matters may include, but are not limited to: (i) intellectual property disputes; (ii) adverse decisions in litigation, including product safety and liability matters, such as the litigation involving Gardasil, consumer protection and commercial cases; (iii) anti-bribery regulations, such as the FCPA, including compliance with ongoing reporting obligations to the government resulting from any settlements; (iv) recalls or withdrawals of pharmaceutical products or forced closings of manufacturing plants; (v) product pricing and promotional matters; (vi) lawsuits, claims and administrative proceedings asserting, or investigations into, violations of securities, antitrust, federal and state pricing, consumer protection, data privacy and other laws and regulations; (vii) environmental, health, safety and sustainability matters, including regulatory actions in response to climate change; and (viii) tax liabilities resulting from assessments from tax authorities.

See Item 8. “Financial Statements and Supplementary Data,” Note 10, “Contingencies and Environmental Liabilities” for more information on the Company’s legal matters.

Product liability insurance for products may be limited, cost prohibitive or unavailable.

As a result of a number of factors, product liability insurance has become less available while the cost of such insurance has increased significantly. The Company is subject to a substantial number of product liability claims. See Item 8. “Financial Statements and Supplementary Data,” Note 10. “Contingencies and Environmental Liabilities” below for more information on the Company’s current product liability litigation. With respect to product liability, the Company self-insures substantially all of its risk, as the availability of commercial insurance has become more restrictive. The Company has evaluated its risks and has determined that the cost of obtaining product liability insurance outweighs the likely benefits of the coverage that is available and, as such, has no insurance for most product liabilities. The Company will continually assess the most efficient means to address its risk; however, there can be no guarantee that insurance coverage will be obtained or, if obtained, will be sufficient to fully cover product liabilities that may arise.

39

Table of Contents

Risks Related to Technology

The Company is increasingly dependent on sophisticated software applications and computing infrastructure, including the use of cloud-based applications and environments. The Company continues to be a target of cyber-attacks that could lead to a disruption of its worldwide operations, including manufacturing, research and sales operations.

The Company is increasingly dependent on sophisticated software applications, complex information technology systems, computing infrastructure, and cloud service providers (collectively, IT systems) to conduct critical operations and financial reporting. Certain of these systems are managed, hosted, provided or used by third parties to assist in conducting the Company’s business. Disruption, degradation, or manipulation of these IT systems through intentional or accidental means by the Company’s employees, third parties with authorized access or unauthorized third parties could adversely affect key business processes. Cyber-attacks against the Company’s IT systems or third-party providers’ IT systems, such as cloud-based systems, could result in exposure of confidential information, the modification of critical data, and/or the failure of critical operations. Misuse of any of these IT systems could result in the disclosure of sensitive personal information or the theft of trade secrets, intellectual property, or other confidential business information. The Company continues to leverage new and innovative technologies across the enterprise to replace outmoded technology and is beginning a multi-year system upgrade of its SAP system and is working to improve the efficacy and efficiency of its business processes, including data acquisition, the use of which can create new risks. In addition, the Company’s Animal Health business sells technology products that, when deployed, could potentially be compromised by a third party and cause disruption both internally and externally.

Although the aggregate impact of cyber-attacks and network disruptions on the Company’s operations and financial condition has not been material to date, the Company continues to be a target of events of this nature and expects them to continue. The Company monitors its data, information technology and personnel usage of Company IT systems to identify and attempt to reduce these risks and continues to do so on an ongoing basis for any current or potential threats. There can be no assurance that the Company’s efforts to protect its data and IT systems or the efforts of third-party providers to protect their IT systems will be successful in preventing disruptions to the Company’s operations, including its manufacturing, research, and sales operations. Such disruptions have in the past and could in the future result in loss of revenue, or the loss of critical or sensitive information from the Company’s or the Company’s third-party providers’ databases or IT systems and have in the past and could in the future also result in financial, legal, business or reputational harm to the Company and substantial remediation costs.

The Company is increasing its use of artificial intelligence (AI) systems to automate processes, analyze data, and support decision-making, which poses inherent risks.

The Company’s growing use of artificial intelligence (AI) systems to automate processes, analyze data, and support decision-making poses inherent risks. Flaws, biases, or malfunctions in these systems could lead to operational disruptions, data loss, or erroneous decision-making, impacting the Company’s business operations, financial condition, and reputation. Ethical and legal challenges may arise, including biases or discrimination in AI outcomes, non-compliance with data protection regulations and emerging laws specifically governing AI systems and tools, such as the European Union AI Act and NIS2 Directive. Unauthorized use of open-source AI tools or generative AI platforms by employees or third parties could result in inadvertent disclosure of confidential information, intellectual property leakage, or regulatory violations.

Furthermore, the deployment of AI systems could expose the Company to increased cybersecurity threats, such as data breaches and unauthorized access leading to financial losses, legal liabilities, and reputational damage. The Company also faces competitive risks if it fails to adopt AI or other machine learning technologies in a timely fashion.

Social media and mobile messaging platforms present risks and challenges.

The inappropriate and/or unauthorized use of certain social media and mobile messaging channels could cause brand damage or information leakage or could lead to legal implications, including from the improper collection and/or dissemination of personally identifiable information. In addition, negative or inaccurate posts or comments about the Company or its products on any social networking platforms could damage the Company’s reputation, brand image and goodwill. Further, the disclosure of non-public Company-sensitive information by the Company’s workforce or others through external media channels could lead to information loss. Although there are internal Company Social Media and Mobile Messaging Policies that guide employees on appropriate personal and professional use of these platforms for communication about the Company, the processes in place may not completely secure and protect information. Identifying potential new points of unauthorized entry as new communication tools expand also presents new challenges.

40

Table of Contents

Cautionary Factors that May Affect Future Results

(Cautionary Statements Under the Private Securities Litigation Reform Act of 1995)

This report and other written reports and oral statements made from time to time by the Company may contain so-called “forward-looking statements,” all of which are based on management’s current expectations and are subject to risks and uncertainties which may cause results to differ materially from those set forth in the statements. One can identify these forward-looking statements by their use of words such as “anticipates,” “expects,” “plans,” “will,” “estimates,” “forecasts,” “projects” and other words of similar meaning, or negative variations of any of the foregoing. One can also identify them by the fact that they do not relate strictly to historical or current facts. These statements are likely to address the Company’s growth strategy, financial results, product approvals, product potential, and development programs. One must carefully consider any such statement and should understand that many factors could cause actual results to differ materially from the Company’s forward-looking statements. These factors include inaccurate assumptions and a broad variety of other risks and uncertainties, including some that are known and some that are not. No forward-looking statement can be guaranteed and actual future results may vary materially. The Company does not assume the obligation to update any forward-looking statement. The Company cautions you not to place undue reliance on these forward-looking statements. Although it is not possible to predict or identify all such factors, they may include the following:

•Competition from generic and/or biosimilar products as the Company’s products lose patent protection.

•Increased “brand” competition in therapeutic areas important to the Company’s long-term business performance.

•The difficulties and uncertainties inherent in development of new product candidates or uses. The outcome of the lengthy and complex process of development of new product candidates and uses is inherently uncertain. A drug candidate can fail at any stage of the process and one or more late-stage product candidates could fail to receive regulatory approval. New product candidates or uses may appear promising in development but fail to reach the market because of efficacy or safety concerns, the inability to obtain necessary regulatory approvals, the difficulty or excessive cost to manufacture and/or the infringement of patents or intellectual property rights of others. Furthermore, the sales of new products may prove to be disappointing and fail to reach anticipated levels.

•Pricing pressures in the public and private sectors, both in the U.S. and abroad, including rules and practices of managed care groups, judicial decisions and governmental laws and regulations related to Medicare, Medicaid and health care reform, pharmaceutical reimbursement and pricing in general.

•Changes in government laws and regulations, including laws governing intellectual property, and the enforcement thereof affecting the Company’s business.

•Efficacy or safety concerns with respect to marketed products, whether or not scientifically justified, leading to product recalls, withdrawals or declining sales.

•Significant changes in customer relationships or changes in the behavior and spending patterns of purchasers of health care products and services, including delaying medical procedures, rationing prescription medications, reducing the frequency of physician visits and foregoing health care insurance coverage.

•Legal factors, including product liability claims, antitrust litigation and governmental investigations, including tax disputes, environmental concerns and patent disputes with branded and generic competitors, any of which could preclude commercialization of products or negatively affect the profitability of existing products.

•Cyber-attacks on the Company’s or third-party providers’ IT systems, which could disrupt the Company’s operations.

•Lost market opportunity resulting from delays and uncertainties in the approval process of the FDA and/or foreign regulatory authorities.

•Increased focus on privacy issues in countries around the world, including the U.S., the EU, and China. The legislative and regulatory landscape for privacy and data protection continues to evolve, and there has been an increasing amount of focus on privacy and data protection issues with the potential to affect directly the Company’s business, including laws in a majority of states in the U.S. requiring security breach notification.

•Changes in tax laws including changes related to the taxation of foreign earnings.

•Changes in accounting pronouncements promulgated by standard-setting or regulatory bodies, including the Financial Accounting Standards Board and the SEC, that are adverse to the Company.

41

Table of Contents

•Economic factors over which the Company has no control, including changes in inflation, interest rates and foreign currency exchange rates.

This list should not be considered an exhaustive statement of all potential risks and uncertainties. See “Risk Factors” above.

Item 1B.Unresolved Staff Comments.

None.

Item 1C. Cybersecurity.

The Company’s cybersecurity measures are primarily focused on ensuring the security and protection of its IT systems and data. The Company’s information security program is managed by a dedicated Chief Information Security Officer (CISO), whose group is responsible for leading enterprise-wide cybersecurity risk management, strategy, policy, standards, architecture, and processes.The Company’s interim CISO has over 22 years of experience in cybersecurity and national security, including distinguished service in the U.S. Army and the National Security Agency. He holds a Master’s degree in Cyber Intelligence Studies and a Bachelor’s degree in Mathematical Physics, and maintains the Certified Information Systems Security Professional (CISSP) credential. Oversight of the information security program remains fully integrated into the Company’s overall enterprise risk management framework.

The CISO provides periodic reports to the Audit Committee (Audit Committee) of the Board of Directors (Board), the full Board, as well as to the Company’s Chief Executive Officer and other members of senior management, as appropriate. These reports include updates on the Company’s cybersecurity risks and threats, the status of projects intended to strengthen its information security systems, assessments of the information security program (including remediation, mitigation, and management of identified vulnerabilities), and the emerging threat landscape. The information security program is regularly evaluated by internal and external consultants and auditors with the results of those reviews reported to senior management and the Audit Committee, which is comprised entirely of independent directors and has oversight responsibility for these risks.

The Company’s information security group monitors the Company’s information systems to prevent, detect, mitigate, and remediate cybersecurity incidents. The Company uses tools and techniques to continually assess and monitor, manage and mitigate cybersecurity threats to its IT systems in a manner consistent with industry practice. The Company engages with key vendors, industry participants, and intelligence and law enforcement communities as part of its continuing efforts to obtain current threat intelligence, collaborate on security enhancements, and evaluate and improve the effectiveness of its information security program. As part of this program, the Company conducts periodic tabletop and red-teaming exercises to assess its cybersecurity incident response processes and defenses. The Company also maintains vendor management diligence and oversight processes to identify and monitor potential risks from cybersecurity threats attendant to its use of third-party service providers.Additionally, the Company monitors cybersecurity threat intelligence received from key third-party service providers associated with the Company.

In the event of a cybersecurity incident, the Company has a process in place whereby members of the information security group will alert the CISO and the CISO will alert the appropriate levels of management, including an incident assessment team, as well as the legal and finance departments so that the materiality of any such event can be assessed in furtherance of fulfilling any reporting requirements. If warranted, senior management will notify the Audit Committee or the full Board, as appropriate.

The Company has been and continues to be the target of cyber-attacks and network disruptions. To date, the risks posed by such cybersecurity threats have not materially affected the Company and its business strategy, results of operations and financial condition, and as of the date of this report, the Company is not aware of any material risks from cybersecurity threats that are reasonably likely to do so, but there can be no assurance that the Company will not be materially affected by such risks in the future. For further information, see Item 1A. “Risk Factors — The Company is increasingly dependent on sophisticated software applications and computing infrastructure. The Company continues to be a target of cyber-attacks that could lead to a disruption of its worldwide operations, including manufacturing, research and sales operations.”

Item 2.Properties.

The Company’s corporate headquarters are located in Rahway, New Jersey. The Company also maintains divisional headquarters in Upper Gwynedd, Pennsylvania. Principal U.S. research facilities are located in Rahway, New Jersey; West Point, Pennsylvania; Boston and Cambridge, Massachusetts; South San Francisco, California; and Elkhorn, Nebraska (Animal Health). Principal research facilities outside the U.S. are located in the United Kingdom,

42

Table of Contents

Switzerland and China. The Company’s manufacturing operations are currently headquartered in Rahway, New Jersey. The Company also has production facilities for human health products at five locations in the U.S. and Puerto Rico. Outside the U.S., through subsidiaries, the Company owns or has an interest in manufacturing plants or other properties in Western Europe, Africa and Asia.

The Company and its subsidiaries own their principal facilities and manufacturing plants under titles that they consider to be satisfactory. The Company believes that its properties are in good operating condition and that its machinery and equipment have been well maintained. The Company believes that its plants for the manufacture of products are suitable for their intended purposes and have capacities and projected capacities, including previously disclosed capital expansion projects, that will be adequate for current and projected needs for existing Company products. Some capacity of the plants is being converted, with any needed modification, to the requirements of newly introduced and future products.

Item 3.Legal Proceedings.

The information called for by this Item is incorporated herein by reference to Item 8. “Financial Statements and Supplementary Data,” Note 10. “Contingencies and Environmental Liabilities.”

Item 4.Mine Safety Disclosures.

Not Applicable.

43

Table of Contents

Executive Officers of the Registrant (ages as of February 1, 2026)

All officers listed below serve at the pleasure of the Board of Directors. None of these officers was elected pursuant to any arrangement or understanding between the officer and any other person(s).

Name Age Offices and Business Experience

On February 2, 2026, the Company announced that Sanat Chattopadhyay, Executive Vice President and President, Merck Manufacturing Division, will retire from the Company, effective July 1, 2026. The Company announced that Mr. David R. Maraldo will assume the role as Executive Vice President and President, Merck Manufacturing Division, effective May 1, 2026, at which time Mr. Maraldo will become, and Mr. Chattopadhyay will cease to be, an Executive Officer of the Company. Mr. Chattopadhyay will remain in a strategic advisory role at the Company until his retirement.

On February 12, 2026, the Company announced that Joseph Romanelli has decided to retire from the Company in the second quarter of 2026.

On February 23, 2026, the Company announced that Brian Foard will join the Company as Executive Vice President, and President Specialty, Pharma & Infectious Diseases, effective March 2, 2026. Mr. Foard most recently served as Executive Vice President and Head of Specialty Care at Sanofi.

44

Table of Contents

PART II

Item 5.Market for Registrant’s Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities.

The principal market for trading of the Company’s Common Stock is the New York Stock Exchange (NYSE) under the symbol MRK.

As of January 31, 2026, there were approximately 80,500 shareholders of record of the Company’s Common Stock.

Issuer purchases of equity securities for the three months ended December 31, 2025 were as follows:

Issuer Purchases of Equity Securities

(1) All shares purchased during the period were made as part of a plan approved by the Board of Directors in January 2025 to purchase up to $10 billion in Merck shares for its treasury.

45

Table of Contents

Performance Graph

The following graph assumes a $100 investment on December 31, 2020, and reinvestment of all dividends, in each of the Company’s Common Stock, the S&P 500 Index, and a composite peer group of major U.S. and European-based pharmaceutical companies, which are: AbbVie Inc., Amgen Inc., AstraZeneca plc, Bristol-Myers Squibb Company, Johnson & Johnson, Eli Lilly and Company, Gilead Sciences Inc., GlaxoSmithKline plc, Novartis AG, Pfizer Inc., Roche Holding AG, and Sanofi SA.

Comparison of Five-Year Cumulative Total Return

Merck & Co., Inc., Composite Peer Group and S&P 500 Index

* Compound Annual Growth Rate

** Peer group average was calculated on a market cap weighted basis as of December 31, 2020.

This Performance Graph will not be deemed to be incorporated by reference into any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934, except to the extent that the Company specifically incorporates it by reference. In addition, the Performance Graph will not be deemed to be “soliciting material” or to be “filed” with the SEC or subject to Regulation 14A or 14C, other than as provided in Regulation S-K, or to the liabilities of section 18 of the Securities Exchange Act of 1934, except to the extent that the Company specifically requests that such information be treated as soliciting material or specifically incorporates it by reference into a filing under the Securities Act or the Exchange Act.

Item 6. [Reserved]

46

Table of Contents

Item 7.Management’s Discussion and Analysis of Financial Condition and Results of Operations.

The following section of this Form 10-K generally discusses 2025 and 2024 results and year-to-year comparisons between 2025 and 2024. Discussion of 2023 results and year-to-year comparisons between 2024 and 2023 that are not included in this Form 10-K can be found in Part II, Item 7. “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2024 filed on February 25, 2025.

Description of Merck’s Business

Merck & Co., Inc. (Merck or the Company) is a global health care company that delivers innovative health solutions through its prescription medicines, including biologic therapies, vaccines and animal health products. The Company’s operations are principally managed on a product basis and include two operating segments, Pharmaceutical and Animal Health, both of which are reportable segments.

The Pharmaceutical segment includes human health pharmaceutical and vaccine products. Human health pharmaceutical products consist of therapeutic and preventive agents, generally sold by prescription, for the treatment of human disorders. The Company sells these human health pharmaceutical products primarily to drug wholesalers and retailers, hospitals, government agencies, and managed health care providers such as health maintenance organizations, pharmacy benefit managers and other institutions. Human health vaccine products consist of preventive pediatric, adolescent and adult vaccines. The Company sells these human health vaccines primarily to physicians, wholesalers, distributors and government entities.

The Animal Health segment discovers, develops, manufactures and markets a wide range of veterinary pharmaceutical and vaccine products, as well as health management solutions and services, for the prevention, treatment and control of disease in all major livestock and companion animal species. The Company also offers an extensive suite of digitally connected identification, traceability and monitoring products. The Company sells its products to veterinarians, distributors, animal producers, farmers and pet owners.

Overview

Financial Highlights

Net Income Attributable to Merck & Co., Inc.:

* > 100%

(1) Non-GAAP net income and non-GAAP earnings per share (EPS) exclude acquisition- and divestiture-related costs, restructuring costs, income and losses from investments in equity securities, and certain other items from Merck’s results prepared in accordance with generally accepted accounting principles in the U.S. (GAAP). For further discussion and a reconciliation of GAAP to non-GAAP net income and EPS, see “Non-GAAP Income and Non-GAAP EPS” below.

Executive Summary

In 2025, Merck successfully advanced its science-led strategy through new product approvals and launches, strong clinical execution, important data readouts, and the addition of novel innovation through business development efforts. The Company also continued to return capital to shareholders, primarily through dividends.

47

Table of Contents

Worldwide sales were $65.0 billion in 2025, an increase of 1% compared with 2024, or 2% excluding the unfavorable effect of foreign exchange. The sales increase was primarily due to growth in oncology, cardiometabolic and respiratory, diabetes, and animal health, largely offset by declines in vaccines, immunology (as Merck’s marketing rights to these products ended in 2024), and virology (driven largely by lower sales of COVID-19 medication Lagevrio).

Merck continues to execute science-led business development transactions to augment its robust internal pipeline and portfolio with compelling external science focused on delivering innovation to patients, long-term growth, and value creation to shareholders. Highlights of 2025 activity include the following:

•Entered into an agreement to acquire Cidara Therapeutics, Inc. (Cidara), a biotechnology company developing drug-Fc conjugate therapeutics, including a long-acting antiviral designed to prevent seasonal and pandemic influenza; this transaction closed in January 2026.

•Acquired Verona Pharma plc (Verona Pharma), a biopharmaceutical company focused on respiratory diseases, through which Merck obtained Ohtuvayre, a product approved for the maintenance treatment of chronic obstructive pulmonary disease (COPD).

•Closed an exclusive license agreement for MK-7262 (HRS-5346), an investigational oral small molecule Lipoprotein(a) inhibitor from Jiangsu Hengrui Pharmaceuticals Co., Ltd. (Hengrui Pharma).

•Closed an agreement with Dr. Falk Pharma GmbH (Falk) to acquire sole global rights to MK-8690, an investigational anti-CD30 ligand monoclonal antibody.

During 2025, Merck continued its efforts to address unmet medical needs by launching Enflonsia in the U.S. for the prevention of respiratory syncytial virus (RSV) lower respiratory tract disease in neonates (newborns) and infants born during or entering their first RSV season. Also in 2025, the Company launched Keytruda Qlex, which was approved by the U.S. Food and Drug Administration (FDA) for subcutaneous administration across all solid tumor indications for Keytruda in the U.S., and the European Commission (EC) approved a new subcutaneous (SC) route of administration and a new pharmaceutical form (solution for injection) of Keytruda (to be marketed as Keytruda SC) for use across all Keytruda indications for adult patients in Europe. Additionally, in pulmonary arterial hypertension (PAH), the Company launched an expanded indication for Winrevair in the U.S. based on the results of the ZENITH trial.

The Company also received numerous other approvals in oncology. Keytruda received approvals for additional indications in certain markets, including in combination with chemotherapy in the therapeutic areas of gastric or gastroesophageal junction (GEJ) adenocarcinoma and malignant pleural mesothelioma, in combination with Padcev (enfortumab vedotin) for locally advanced or metastatic urothelial carcinoma and for cisplatin-ineligible muscle-invasive bladder cancer (MIBC), as well as in combination with radiotherapy with or without chemotherapy for head and neck squamous cell carcinoma (HNSCC). Additionally, in 2025, Welireg was approved in the European Union (EU) and Japan for the treatment of adult patients with certain von Hippel-Lindau (VHL) disease-associated tumors and certain adult patients with renal cell carcinoma (RCC), as well as in the U.S. for certain adult and pediatric patients with pheochromocytoma and paraganglioma.

In addition to the regulatory approvals discussed above, the Company advanced its late-stage pipeline with several regulatory submissions.

•MK-8591A, doravirine/islatravir, is an investigational, once-daily, oral two-drug regimen for adults with HIV-1 infection that is virologically suppressed on antiretroviral therapy under review by the FDA. MK-8591A is also under review in Japan.

•MK-1654, Enflonsia, a prophylactic long-acting monoclonal antibody designed to protect infants from RSV disease during their first RSV season, is under review in the EU and Japan.

48

Table of Contents

•MK-7962, Winrevair, an activin signaling inhibitor for the treatment of adults with PAH (World Health Organization [WHO] Group 1 pulmonary hypertension), is under review by the FDA in connection with a proposed update to the U.S. product label based on the results of the HYPERION trial.

•MK-3475, Keytruda (pembrolizumab), is an anti-PD-1 (programmed death receptor-1) therapy available for intravenous administration. MK-3475A, Keytruda Qlex,combines pembrolizumabwith berahyaluronidase alfa to enhance dispersion and permeability to enable subcutaneous administration. Keytruda and Keytruda Qlex each are approved for the treatment of many cancers and continue to be studied in additional Phase 3 trials.

◦Keytruda is under review in the EU and Japan in combination with chemotherapy with or without bevacizumab for the treatment of certain patients with platinum-resistant recurrent ovarian cancer.

◦Keytruda is also under review in the EU and Japan in combination with Pfizer, Inc.’s (Pfizer) and Astellas’ Padcev as neoadjuvant treatment, then continued after radical cystectomy as adjuvant treatment, for patients with MIBC who are ineligible for cisplatin-based chemotherapy.

◦Keytruda and Keytruda Qlex are under review by the FDA in combination with Gilead Sciences Inc.’s (Gilead) sacituzumab govitecan (Trodelvy) for the first-line treatment of certain patients with unresectable locally advanced or metastatic triple-negative breast cancer (TNBC) whose tumors express programmed death-ligand 1 (PD‐L1).

•MK-6482, Welireg, is Merck’s first-in-class oral hypoxia-inducible factor-2 alpha (HIF-2α) inhibitor.

◦Welireg, in combination with Keytruda or Keytruda Qlex, is under priority review by the FDA for the adjuvant treatment of certain patients with clear cell RCC following nephrectomy.

◦Welireg, in combination with MK-7902, Lenvima, an orally available multiple receptor tyrosine kinase inhibitor (TKI), is under review by the FDA for the treatment of certain patients with advanced RCC following previous treatment with a PD-1 or PD-L1 inhibitor. Lenvima is being developed as part of a collaboration with Eisai Co., Ltd. (Eisai).

In 2025, the Company announced positive late-stage results from 18 Phase 3 trials and initiated 21 new Phase 3 trials spanning cardiometabolic and respiratory, immunology, infectious diseases, oncology and ophthalmology. The Company now has approximately 80 Phase 3 studies underway. The Company is diversifying its oncology portfolio and executing on its strategy which is broadly based on three strategic pillars: immuno-oncology, precision molecular targeting and tissue targeting. Merck has numerous Phase 3 oncology programs within these pillars.

Immuno-oncology

•V940 (mRNA-4157), intismeran autogene, is an investigational individualized neoantigen therapy being evaluated in combination with Keytruda for the adjuvant portion of treatment in patients with certain types of melanoma and non-small cell lung cancer (NSCLC). Intismeran autogene is being developed as part of a collaboration with Moderna, Inc. (Moderna).

•MK-1308A is the coformulation of quavonlimab, Merck’s novel investigational anti-cytotoxic T-lymphocyte associated protein 4 (CTLA-4) antibody, in combination with pembrolizumab, being evaluated for the treatment of RCC.

Precision molecular targeting

•MK-1026, nemtabrutinib, is an investigational oral, reversible, non-covalent Bruton’s tyrosine kinase (BTK) inhibitor, being evaluated for the treatment of hematological malignancies, including chronic lymphocytic leukemia and small lymphocytic lymphoma.

•MK-1084, calderasib, is an investigational oral selective KRAS G12C inhibitor being evaluated with or without Keytruda or Keytruda Qlex for the treatment of certain patients with colorectal and non-small cell lung cancers. Calderasib is being developed as part of a collaboration with Taiho Pharmaceutical Co. Ltd. and Astex Pharmaceuticals (UK), a wholly owned subsidiary of Otsuka Pharmaceutical Co., Ltd.

•MK-3543, bomedemstat, is an investigational orally available lysine-specific demethylase 1 inhibitor being evaluated for the treatment of certain patients with essential thrombocythemia.

•MK-5684, opevesostat, is an investigational cytochrome P450 11A1 (CYP11A1) inhibitor being evaluated for the treatment of certain patients with metastatic castration-resistant prostate cancer.

•MK-6482, Welireg, is being developed for expanded indications in RCC in combination with Keytruda and Lenvima, and in other combinations.

49

Table of Contents

•MK-7339, Lynparza, is an oral poly (ADP-ribose) polymerase (PARP) inhibitor being evaluated in combination with Keytruda for expanded indications in the therapeutic areas of non-small cell lung and small cell lung cancers. Lynparza is being developed as part of a collaboration with AstraZeneca PLC (AstraZeneca).

Tissue targeting

•MK-1022, patritumab deruxtecan, is an investigational human epidermal growth factor receptor 3 (HER3) directed antibody drug conjugate (ADC) being evaluated in certain patients with breast cancer. Patritumab deruxtecan is being developed as part of a collaboration with Daiichi Sankyo.

•MK-2140, zilovertamab vedotin, is an investigational ADC targeting receptor tyrosine kinase-like orphan receptor 1 (ROR1) being evaluated for the treatment of hematological malignancies, including diffuse large B cell lymphoma.

•MK-2400, ifinatamab deruxtecan, is an investigational B7-H3 directed ADC being evaluated in certain patients with esophageal, prostate, and small cell lung cancers. Ifinatamab deruxtecan is being developed as part of a collaboration with Daiichi Sankyo.

•MK-2870, sacituzumab tirumotecan, is an investigational trophoblast cell-surface antigen 2 (TROP2)-directed ADC being evaluated for certain patients with breast, cervical, endometrial, gastric, non-small cell lung, and ovarian cancers. Sacituzumab tirumotecan is being developed as part of a collaboration with Kelun-Biotech.

•MK-5909, raludotatug deruxtecan, is an investigational CDH6 targeting ADC being evaluated in patients with platinum resistant ovarian cancer. Raludotatug deruxtecan is being developed as part of a collaboration with Daiichi Sankyo.

Additionally, the Company currently has candidates in Phase 3 clinical development in several other therapeutic areas.

•MK-0616, enlicitide decanoate, is an investigational oral proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor being evaluated for the treatment of hypercholesterolemia, including in studies evaluating low-density lipoprotein cholesterol reduction and a cardiovascular outcomes study.

•V181 is an investigational quadrivalent vaccine for the prevention of dengue disease caused by any of the four dengue virus serotypes (DENV-1, DENV-2, DENV-3, and DENV-4), regardless of prior dengue exposure.

•MK-3000 is an investigational, potentially first-in-class tetravalent, tri-specific antibody that acts as an agonist of the Wingless-related integration site signaling pathway, which is in clinical development for the treatment of diabetic macular edema.

•MK-8591D is an investigational once-weekly, oral combination of Merck’s islatravir, a nucleoside analog leveraging translocation inhibition, and Gilead’s lenacapavir being evaluated for the treatment of HIV-1 infection in virologically suppressed adults (which remains under a partial clinical hold for any studies that would use islatravir doses higher than the doses considered for the revised clinical programs).

•MK-8527 is an investigational once-monthly, oral nucleoside analog leveraging translocation inhibition, for HIV-1 pre-exposure prophylaxis (PrEP).

•MK-1406 (formerly CD388) is an investigational small molecule neuraminidase inhibitor stably conjugated to a proprietary Fc fragment of a human antibody designed to prevent seasonal and pandemic influenza. MK-1406 was obtained in connection with the January 2026 acquisition of Cidara.

•MK-7240, tulisokibart, is an investigational humanized monoclonal antibody directed to tumor necrosis factor-like ligand 1A, a central amplifier of inflammatory pathways and fibrotic mechanisms in inflammatory bowel disease, being evaluated for the treatment of Crohn’s disease and ulcerative colitis.

•MK-4482, Lagevrio, is an investigational oral antiviral medicine for the treatment of mild to moderate COVID-19 in adults who are at risk for progressing to severe disease, which is reflected in Phase 3 development in the U.S. as it remains investigational following FDA Emergency Use Authorization (EUA) in 2021. Merck is developing Lagevrio as part of a collaboration with Ridgeback Biotherapeutics LP (Ridgeback).

Merck’s capital allocation strategy continues to prioritize investments in its business to drive near- and long-term growth, including investing in the Company’s key growth drivers and its broad and diverse pipeline of novel candidates, enabled in part by the benefits of the Company’s multiyear optimization initiative. Research and development expenses in 2025 reflect increased development spending particularly in the therapeutic areas of ophthalmology, oncology and immunology. In addition, Merck remains committed to its dividend and will continue to

50

Table of Contents

pursue the most compelling external science and technologies through value-enhancing business development transactions.

In November 2025, Merck’s Board of Directors approved an increase to the Company’s quarterly dividend, raising it to $0.85 per share from $0.81 per share on the Company’s outstanding common stock. During 2025, the Company returned $13.3 billion to shareholders through dividends of $8.2 billion and share repurchases of $5.1 billion. In January 2025, Merck’s Board of Directors authorized a new share repurchase program of up to $10 billion of Merck’s common stock for its treasury.

GAAP and non-GAAP EPS were negatively affected in 2025, 2024 and 2023 by $0.20, $1.28, and $6.21, respectively, of per share charges for certain upfront and pre-approval milestone payments related to collaborations and licensing agreements, as well as charges related to pre-approval assets obtained in transactions accounted for as asset acquisitions.

Pricing

Global efforts toward health care cost containment continue to exert pressure on product pricing and market access worldwide. Changes to the U.S. health care system as part of health care reform, as well as increased purchasing power of entities that negotiate on behalf of Medicare, Medicaid, and private sector beneficiaries, have contributed to pricing pressure.

In 2021, the U.S. Congress passed the American Rescue Plan Act, which included a provision that eliminated the statutory cap on rebates drug manufacturers pay to Medicaid beginning in January 2024. As a result of this provision, the Company paid state Medicaid programs more in rebates than it received on Medicaid sales of Januvia, Janumet and Janumet XR in 2024.

In 2022, the U.S. Congress passed the Inflation Reduction Act (IRA), which made significant changes to how drugs are covered and paid for under the Medicare program, including the creation of financial penalties for drugs whose prices rise faster than the rate of inflation, redesign of the Medicare Part D program to require manufacturers to bear more of the liability for certain drug benefits (which went into effect in 2025), and government price setting for certain Medicare Part D drugs (starting in 2026) and Medicare Part B drugs (starting in 2028). The U.S. Department of Health and Human Services (HHS), through the Centers for Medicare & Medicaid Services (CMS), selected Januvia in 2023 for the first year of the IRA’s “Drug Price Negotiation Program” (Program), and selected Janumet and Janumet XR in 2025 for the second year of the IRA’s Program. Pursuant to the IRA’s Program, the government set a price for Januvia, which became effective on January 1, 2026, and set a price for Janumet and Janumet XR, which will become effective on January 1, 2027. In addition, in January 2026, HHS announced that Lenvima has been selected for government price setting, the set price for which will become effective on January 1, 2028. Furthermore, the Company expects that Keytruda will be selected in 2027 for government price setting, which would become effective on January 1, 2029. Government price setting may also impact pricing in the private market negatively affecting the Company’s performance. The Company has sued the U.S. government regarding the IRA’s Program (see Note 10 to the consolidated financial statements).

51

Table of Contents

Additionally, increased utilization of the 340B Federal Drug Discount Program and restrictions on the Company’s ability to identify inappropriate discounts are having a negative impact on Company performance. Furthermore, the Executive Branch and Congress continue to discuss legislation designed to control health care costs, including the cost of drugs. In several international markets, government-mandated pricing actions have reduced prices of generic and patented drugs. In addition, the Company’s sales performance in 2025 was negatively affected by other cost-reduction measures taken by governments and other third parties to lower health care costs.

The Company anticipates all of these actions and additional actions in the future will continue to negatively affect sales and profits.

In May 2025, the U.S. presidential administration issued an executive order intended to encourage or impose the use of “most-favored-nation” pricing to tie U.S. prescription drug prices to prices in selected comparably developed nations. In July 2025, the Company and other pharmaceutical companies received letters from the U.S. presidential administration with a request to agree to the administration’s “most-favored-nation” drug pricing goals by September 29, 2025. Further to the letter received from the administration, in December 2025, the Company announced that it had entered into a three-year agreement (MFN Agreement) with the U.S government that addressed the four policy goals of the administration’s July letter. Included within the MFN Agreement is an obligation by the Company to provide key products through a direct-to-patient program at affordable prices for eligible patients in the U.S. This will initially include Januvia, Janumet and Janumet XR, and will be expanded in the future to include enlicitide decanoate pending FDA approval. The Company also agreed to offer its existing medicines at discounted prices to Medicaid, excluding certain products. The Company has also agreed that products launched during the term of the MFN Agreement (with certain exceptions) will be subject to “most-favored-nation” pricing in reference to prices for such products in a specified group of countries (MFN Countries). Finally, the Company agreed to repatriate and share with the Federal government a portion of foreign revenue received by the Company as a result of the government’s successful trade policy efforts. Additionally, the Company reached an agreement with the U.S. Department of Commerce to delay Section 232 tariffs for three years, enabling the Company to make investments in the U.S. to reshore manufacturing for American patients.

Operating Results

Sales

Worldwide sales were $65.0 billion in 2025, representing growth of 1% compared with 2024, or 2% excluding the unfavorable effect of foreign exchange. Global sales growth was primarily due to higher sales in the oncology franchise, largely due to the performance of Keytruda and Welireg, as well as increased alliance revenue from Koselugo (resulting from an amendment to the collaboration agreement), Reblozyl, and Lynparza. Also contributing to revenue growth in 2025 were higher sales in the cardiometabolic and respiratory franchise, largely attributable to the ongoing launch of Winrevair, as well as the inclusion of Ohtuvayre sales following the October 2025 acquisition of Verona Pharma. Growth in the diabetes franchise largely attributable to higher net pricing of Januvia, and higher sales of animal health products largely due to the performance of livestock products also drove sales growth. Revenue growth in 2025 was largely offset by lower sales in the vaccines franchise primarily due to Gardasil/Gardasil 9, partially offset by the ongoing launch of Capvaxive and the U.S. launch of Enflonsia.Revenue growth in 2025 was also offset by lower sales in the immunology franchise due to the return of the marketing rights for Remicade and Simponi in former Merck territories to Johnson & Johnson on October 1, 2024, and by lower sales in the virology franchise largely attributable to Lagevrio.

Sales in the U.S. grew 13% to $36.5 billion in 2025 primarily driven by higher sales of Keytruda, Winrevair, Capvaxive, Januvia, Bridion, Gardasil 9, Welireg, Janumet, and Prevymis. The inclusion of Ohtuvayre sales, higher alliance revenue from Reblozyl, and higher sales of animal health products also contributed to U.S. revenue growth. U.S. sales growth in 2025 was partially offset by lower sales of Dificid and Lagevrio.

International sales declined 11% in 2025, or 10% excluding the unfavorable effect of foreign exchange. The international sales decline was primarily due to lower sales of Gardasil/Gardasil 9,Simponi, Lagevrio, Januvia, Bridion,Remicade, and Janumet,partially offset by higher sales of Keytruda, Prevymis, Winrevair, increased alliance revenue from Koselugo and Lynparza, as well as higher sales of animal health products. International sales represented 44% and 50% of total sales in 2025 and 2024, respectively.

52

Table of Contents

See Note 18 to the consolidated financial statements for details on sales of the Company’s products. A discussion of performance for select products in the franchises follows.

Pharmaceutical Segment

Oncology

* > 100%

(1) Alliance revenue for Lynparza and Lenvima represents Merck’s share of profits, which are product sales net of cost of sales and commercialization costs (see Note 4 to the consolidated financial statements).

(2) Alliance revenue for Reblozyl represents royalties (see Note 4 to the consolidated financial statements).

(3) Alliance revenue for Koselugo in 2025 primarily includes a $150 million upfront payment received and $175 million of regulatory approval milestones recorded in connection with an amendment to the collaboration agreement with AstraZeneca, which revised the payment structure. Alliance revenue in 2024 and 2023 represents Merck’s share of profits, which are product sales net of cost of sales and commercialization costs. See Note 4 to the consolidated financial statements for more information.

Keytruda is an anti-PD-1 therapy that has been approved in over 40 indications in the U.S., including 19 tumor types and 2 tumor-agnostic indications, and has similarly been approved in markets worldwide for many of these indications. The Keytruda clinical development program includes studies across a broad range of cancer types.

Keytruda Qlex is a subcutaneously-administered fixed combination of pembrolizumab and berahyaluronidase alfa, which enhances dispersion and permeability to enable subcutaneous administration of pembrolizumab. Keytruda Qlex, which was initially approved by the FDA in September 2025, is approved in the U.S. in solid tumor indications approved for Keytruda. In November 2025, the EC approved a new subcutaneous (SC) route of administration and a new pharmaceutical form (solution for injection) of Keytruda (to be marketed as Keytruda SC) for use across Keytruda indications for adults in Europe. Timing for commercial availability of Keytruda SC in individual EU countries will depend on multiple factors, including the completion of national reimbursement procedures and the outcome of litigation with Halozyme, Inc. as discussed in Note 10 to the consolidated financial statements.

Combined global sales of Keytruda/Keytruda Qlex grew 7% in 2025. Sales growth in the U.S. reflects higher demand and net pricing, partially offset by a negative impact due to the timing of purchases. Increased demand in the U.S. was driven by higher utilization across earlier-stage indications, including in certain types of cervical cancer, TNBC, NSCLC, RCC, and HNSCC, as well as higher demand across multiple approved metastatic indications, in particular for the treatment of certain types of urothelial and endometrial cancers. Sales growth in international markets reflects increased uptake predominately for the TNBC, NSCLC, and RCC earlier-stage indications, as well as higher demand in urothelial, gastric, cervical, and endometrial cancer metastatic indications. The 2025 launch and reimbursement of new indications for Keytruda in the EU had a negative impact on pricing in those markets. In addition, a biosimilar of Keytruda has launched in Argentina.

Summarized below are the Keytruda regulatory approvals received in 2025 and, to date, in 2026.

Date Approval

53

Table of Contents

Summarized below are the KeytrudaQlex regulatory approvals received in 2025 and, to date, in 2026.

Date Approval

The Company is a party to license agreements pursuant to which the Company pays royalties on net sales of Keytruda. Under the terms of the more significant of these agreements, Merck paid a royalty of 6.5% on worldwide net sales of Keytruda through December 2023 to one third party, which declined to 2.5% in 2024. This royalty (which also applies to net sales of Keytruda Qlex) will continue through 2026, terminating thereafter. The Company pays an additional 2% royalty on worldwide net sales of Keytruda (and on Keytruda Qlex following regulatory approval) to another third party; this royalty expired in the U.S. in September 2024, expired in major European markets in the second half of 2025, but will continue to be paid on net sales of Keytruda and Keytruda Qlex in certain other international markets expiring at various dates through 2035. The royalty expenses are included in

54

Table of Contents

Cost of sales. The Company may be subject to additional royalties on net sales of Keytruda Qlex in the future under certain circumstances (see Note 3 to the consolidated financial statements).

Lynparza is a PARP inhibitor being developed and commercialized as part of a collaboration with AstraZeneca (see Note 4 to the consolidated financial statements). Lynparza is approved for the treatment of certain types of advanced or recurrent ovarian, early or metastatic breast, metastatic pancreatic and metastatic castration-resistant prostate cancers. Alliance revenue related to Lynparza grew 11% in 2025 largely due to higher demand globally. In January 2025, China’s NMPA approved Lynparza as adjuvant treatment for adult patients with germline BRCA-mutated, HER2-negative high-risk early breast cancer, based on the OlympiA trial.

Lenvima is an oral receptor TKI being developed and commercialized as part of a collaboration with Eisai (see Note 4 to the consolidated financial statements). Lenvima is approved for the treatment of certain types of thyroid cancer, RCC, HCC, in combination with everolimus for certain patients with advanced RCC, and in combination with Keytruda for certain patients with advanced endometrial carcinoma or advanced RCC. Alliance revenue related to Lenvima grew 4% in 2025 primarily due to higher sales in the U.S. reflecting increased demand that was partially offset by lower pricing.

Sales of Welireg, for the treatment of adult patients with certain VHL disease-associated tumors, certain adult patients with previously treated advanced RCC, and certain patients with pheochromocytoma and paraganglioma, rose 41% in 2025 primarily due to higher demand in the U.S. and continued launch uptake in several international markets, partially offset by lower net pricing in the U.S. (largely due to the Medicare Part D redesign that was part of the IRA).

Welireg received the following regulatory approvals in 2025.

Date Approval

The EC conditional approvals of Welireg noted above will be valid for one year, subject to yearly renewal, pending certain additional clinical data. Timing for commercial availability of Welireg in individual EU countries will depend on multiple factors, including the completion of national reimbursement procedures.

Reblozyl is a first-in-class erythroid maturation recombinant fusion protein that is being commercialized through a global collaboration with Bristol Myers Squibb Company (BMS) (see Note 4 to the consolidated financial statements). Reblozyl is approved for the treatment of anemia in certain rare blood disorders. Alliance revenue related to this collaboration (consisting of royalties) increased 41% in 2025 due to strong underlying sales performance.

Koselugo is an oral, selective MEK inhibitor approved for the treatment of patients with neurofibromatosis type 1 who have symptomatic inoperable plexiform neurofibromas. Koselugo is part of a collaboration with AstraZeneca. The increase in alliance revenue in 2025 is due to the recognition of a $150 million upfront payment received and $175 million of regulatory approval milestones recorded in connection with an amendment to the collaboration agreement that (subject to an annual election by AstraZeneca) discontinued the revenue and cost sharing provisions of the collaboration, and changed the payment structure. See Note 4 to the consolidated financial statements for additional information.

55

Table of Contents

Vaccines

Capvaxive 759 * * 97 — — —

Enflonsia 100 — — — — — —

* > 100%

In January 2026, the acting director of the U.S. Centers for Disease Control and Prevention (CDC) announced changes to the child and adolescent immunization schedule (January announcement), reducing the number of routinely recommended vaccinations and creating three new categories: immunizations recommended for all children; immunizations recommended for certain high-risk groups or populations; and immunizations based on shared clinical decision-making. Immunizations recommended for all children include vaccines for measles, mumps, rubella, polio, pertussis, tetanus, diphtheria, Haemophilus influenzae type B (Hib), pneumococcal disease, human papillomavirus (HPV), and varicella (chickenpox). Immunizations recommended for certain high-risk groups or populations include RSV, hepatitis A, hepatitis B, and dengue. Immunizations recommended based on shared clinical decision-making include rotavirus, hepatitis A, and hepatitis B. HHS has stated that immunizations for all of the diseases covered by the previous immunization schedule will still be available to anyone who wants them through Affordable Care Act insurance plans and federal insurance programs, including Medicaid, the Children’s Health Insurance Program, and the Vaccines For Children (VFC) program. Additionally, in September 2025, the trade association representing U.S. health insurers (AHIP) announced that its member health plans would continue to cover all immunizations that had been recommended by the CDC’s Advisory Committee on Immunization Practices (ACIP) as of September 1, 2025, with no cost-sharing for patients through the end of 2026.

Combined worldwide sales of Gardasil and Gardasil 9, vaccines to help prevent certain cancers and other diseases caused by certain types of HPV, declined 39% in 2025 primarily driven by lower demand in China (discussed below), and in Japan reflecting in part that the last date to initiate the first dose in Japan’s national immunization program catch-up cohort was in March 2025. The declines were partially offset by higher sales in the U.S. due to higher net pricing and favorable CDC purchasing patterns. Higher demand and timing in certain international markets also partially offset the sales decline in 2025. Beginning in mid-2024, the Company observed a significant decline in shipments from its distributor and commercialization partner in China, Chongqing Zhifei Biological Products Co., Ltd. (Zhifei), to disease and control prevention institutions and correspondingly into the points of vaccination compared with prior quarters of 2024, resulting in above normal inventory levels at Zhifei. Accordingly, the Company shipped less than its contracted doses to Zhifei in the latter part of 2024. Lower demand in China persisted and, at the end of 2024, overall channel inventory levels in China remained elevated at above normal levels. Therefore, the Company made a decision to temporarily pause shipments to China beginning in February 2025 and, given continued lower demand and elevated inventory levels in China, in mid-2025, the Company determined it would not make any further shipments to China in 2025. The Company will not resume shipments to China until inventory levels return to normal and cannot predict when this will occur. In January 2025, China’s NMPA approved Gardasil for use in males 9-26 years of age to help prevent certain HPV-related cancers and diseases. In April 2025, China’s NMPA approved Gardasil 9 for use in males 16-26 years of age to help prevent certain HPV-related cancers and diseases. In May 2025, a nine-valent HPV vaccine produced by a local manufacturer received regulatory approval in China for use in females 9-45 years of age. In August 2025, the Company’s nine-valent HPV vaccine was approved for use in males nine years of age and older in Japan where it will be marketed as Silgard 9.

Among the changes in the CDC’s January announcement referenced above was a reduction of the recommended doses for HPV vaccination of adolescents to a single dose. Gardasil 9is currently indicated in the U.S. for a two-dose regimen in adolescents aged 9-14 and a three-dose regimen for those aged 15-45. Previous CDC recommendations for adolescents followed FDA-approved dosing. Many countries outside the U.S. have implemented a reduced dosing schedule for HPV vaccination in certain age groups. The Company anticipates that any negative effect of these recommendations or reduced dosing schedules on sales of Gardasil/Gardasil 9 will not be material.

56

Table of Contents

The Company is a party to license agreements pursuant to which the Company pays royalties on net sales of Gardasil/Gardasil 9. Under the terms of the more significant of these agreements, Merck pays a 7% royalty on net sales of Gardasil/Gardasil 9 in the U.S. to one third party (this royalty expires in December 2028). Merck paid an additional 7% royalty on worldwide net sales of Gardasil/Gardasil 9 to another third party; this royalty expired in December 2023. The royalty expenses are included in Cost of sales.

Global sales of ProQuad, a pediatric combination vaccine to help protect against measles, mumps, rubella and varicella, grew 1% in 2025 primarily due to higher demand in Europe, partially offset by lower sales in the U.S. reflecting lower demand that was partially offset by higher net pricing. As a result of manufacturing delays, in January 2025, the Company borrowed doses of ProQuad from the CDC Pediatric Vaccine Stockpile (CDC Stockpile), which were used to support routine vaccination in the U.S. The Company replenished the borrowing later in 2025. Worldwide sales of M-M-R II, a vaccine to help protect against measles, mumps and rubella, grew 3% in 2025 primarily due to higher sales in the U.S., largely reflecting higher net pricing and increased demand, partially offset by lower demand in certain international markets. Global sales of Varivax, a vaccine to help prevent chickenpox (varicella), declined 6% in 2025 primarily attributable to lower sales in the U.S., largely driven by lower demand and unfavorable CDC Stockpile activity, partially offset by higher net pricing. The unfavorable impact to Varivax sales from CDC Stockpile activity was offset by CDC Stockpile activity for other products as noted below. The Varivax sales decline was also due in part to lower demand in the Asia Pacific region. Higher demand in Latin America partially offset the Varivax sales decline in 2025.

In September 2025, the ACIP voted to recommend that children under the age of four years receive protection from chickenpox (varicella) as a standalone immunization rather than in combination with measles, mumps, and rubella (MMR) vaccination, eliminating a previous shared clinical decision-making recommendation that allowed parents to choose combined MMR and varicella vaccine (MMRV) first-dose administration. The ACIP also voted to align the VFC program with this change. The acting CDC Director adopted the recommendation in October 2025. MMR and varicella vaccines remain recommended and funded through the VFC program for both the first and second doses. The Company is the only manufacturer in the U.S. of MMRV vaccine (ProQuad) and varicella vaccine (Varivax). The Company anticipates that any negative effect of these recommendations on sales of ProQuad will not be material.

Worldwide sales of Vaxneuvance, a vaccine to help protect against invasive pneumococcal disease caused by certain serotypes, rose 2% in 2025 primarily due to higher demand in Europe and certain markets in the Asia Pacific region, partially offset by lower demand in Japan and the Latin America region due to competition. U.S. sales of Vaxneuvance were nearly flat year over year as a benefit from public and private sector purchasing patterns in the U.S. was offset by lower demand due to competition. U.S. Vaxneuvance sales in 2025 benefited from approximately $70 million of favorable CDC Stockpile activity, of which approximately $60 million was offset by a drawdown of CDC Stockpile inventory for Varivax (noted above) and RotaTeq, which resulted in a net neutral transaction. Merck is a party to license agreements pursuant to which the Company pays royalties on sales of Vaxneuvance. Under the most significant of these agreements, Merck pays a royalty of 7.25% on net sales of Vaxneuvance through 2026; this royalty will decline to 2.5% on net sales from 2027 through 2035. The royalty expenses are included in Cost of sales.

Sales of Capvaxive, a vaccine for the prevention of invasive pneumococcal disease and pneumococcal pneumonia caused by certain serotypes in individuals 18 years of age and older, increased to $759 million in 2025 primarily due to continued uptake following launch in the U.S. in 2024. Capvaxive sales growth in 2025 also reflects early launch uptake in certain international markets. Capvaxive was approved in the U.S. in June 2024, in the EU in March 2025, and in Japan in August 2025. The timing of availability of Capvaxive in individual EU countries will depend on multiple factors including the completion of national reimbursement procedures. Merck is a party to license agreements pursuant to which the Company pays royalties on sales of Capvaxive. Under the terms of the most significant of these agreements, Merck pays a royalty of 7.25% on net sales of Capvaxive through 2026; this royalty will decline to 2.5% on net sales from 2027 through 2035. The royalty expenses are included in Cost of sales.

Worldwide sales of Pneumovax 23, a vaccine to help prevent pneumococcal disease, declined 37% in 2025 due to lower global demand, particularly in the U.S. and Europe, as the market has shifted toward newer adult pneumococcal conjugate vaccines.

In June 2025, the FDA approved Enflonsia, a preventive, long-acting monoclonal antibody, for the prevention of RSV lower respiratory tract disease in neonates (newborns) and infants who are born during or entering their first RSV season. Also in June 2025, the ACIP voted to recommend Enflonsia as an option for the prevention of RSV lower respiratory tract disease in infants younger than eight months of age who are born during or entering their first RSV season. These provisional recommendations were adopted by the CDC Director and are now official. The

57

Table of Contents

ACIP also voted to include Enflonsia in the VFC program. Sales of Enflonsia in 2025 were due in part to inventory stocking.

Hospital Acute Care

Global sales of Bridion, for the reversal of two types of neuromuscular blocking agents used during surgery, grew 4% in 2025 as higher demand and net pricing in the U.S. was partially offset by lower demand in most international markets due to generic competition. Bridion will lose market exclusivity in the U.S. in July 2026 at which time the Company anticipates a significant and rapid decline in U.S. sales of Bridion. The Company expects to discontinue U.S. sales of Bridion by the end of 2026.

Worldwide sales of Prevymis, a medicine for prophylaxis (prevention) of cytomegalovirus (CMV) infection and disease in certain high risk adult and pediatric recipients of an allogenic hematopoietic stem cell transplant and for prophylaxis of CMV disease in certain high risk adult and pediatric recipients of a kidney transplant, grew 25% in 2025 largely due to higher demand in the U.S. and in most international markets reflecting in part the launch of new indications, partially offset by lower demand in China due to generic competition.

Worldwide sales of Dificid, a medicine for the treatment of C. difficile-associated diarrhea, declined 27% in 2025 due to generic competition in the U.S. Dificid lost market exclusivity in the U.S. in July 2025; accordingly, the Company is experiencing a significant decline in U.S. sales of Dificid and expects the decline to continue.

Cardiometabolic and Respiratory

Ohtuvayre 178 — — — — — —

* > 100%

(1) Alliance revenue for Adempas and Verquvo represents Merck’s share of profits from sales in Bayer’s marketing territories, which are product sales net of cost of sales and commercialization costs (see Note 4 to the consolidated financial statements).

Winrevair is an activin signaling inhibitor indicated for the treatment of adults with PAH (WHO Group 1 pulmonary hypertension) to improve exercise capacity and WHO functional class (FC), and reduce the risk of clinical worsening events including hospitalization for PAH, lung transplantation and death. Sales of Winrevair rose to $1.4 billion in 2025 primarily reflecting higher sales in the U.S. due to continued uptake since launch, partially offset by lower net pricing in the U.S. (largely due to the Medicare Part D redesign that was part of the IRA). Sales growth also reflects early launch uptake in certain international markets, particularly in the EU and Japan. Winrevair was originally approved in the U.S. in March 2024, in the EU in August 2024, and in Japan in June 2025 (where it is being marketed as Airwin). Winrevair is the subject of a licensing agreement pursuant to which Merck pays a 22% royalty on net sales of Winrevair to BMS. The royalty expenses are included in Cost of sales.

Summarized below are the Winrevair regulatory approvals received in 2025 and, to date, in 2026.

Date Approval

58

Table of Contents

Adempas and Verquvo are part of a worldwide collaboration with Bayer AG (Bayer) to market and develop soluble guanylate cyclase (sGC) modulators (see Note 4 to the consolidated financial statements). Adempas is approved for the treatment of certain types of PAH and chronic pulmonary hypertension. Verquvo is approved to reduce the risk of cardiovascular death and heart failure hospitalization following a hospitalization for heart failure or need for outpatient intravenous diuretics in adults with symptomatic chronic heart failure and reduced ejection fraction. Alliance revenue from the collaboration grew 13% in 2025 reflecting higher demand in Bayer’s marketing territories. The Company expects alliance revenue will decline in 2026 reflecting the loss of market exclusivity for Adempas in the U.S. Revenue also includes sales of Adempas and Verquvo in Merck’s marketing territories. Sales of Adempas in Merck’s marketing territories grew 9% in 2025 primarily due to higher demand.

Ohtuvayre is an inhaled phosphodiesterases 3 and 4 (PDE3 and PDE4) inhibitor, which was approved in the U.S. in June 2024 for the maintenance treatment of COPD in adults. Ohtuvayre was obtained in conjunction with Merck’s October 2025 acquisition of Verona Pharma. Sales of Ohtuvayre recorded by Merck following the closing of the transaction were $178 million in 2025.

Virology

Lagevrio is an investigational oral antiviral COVID-19 medicine being developed in a collaboration with Ridgeback (see Note 4 to the consolidated financial statements). Sales of Lagevrio declined 61% in 2025 largely due to lower demand in several markets in the Asia Pacific region, particularly in Japan, and in the U.S. driven primarily by declining COVID-19 cases. The Company expects the Lagevrio sales decline to continue in 2026.

Immunology

Simponi and Remicade are treatments for certain inflammatory diseases that the Company marketed in Europe, Russia and Türkiye. The Company’s marketing rights with respect to these products reverted to Johnson & Johnson on October 1, 2024, subsequent to which the Company stopped recognizing sales of these products.

Diabetes

Worldwide combined sales of Januvia and Janumet, medicines that help lower blood sugar levels in adults with type 2 diabetes, grew 12% in 2025 primarily due to higher net pricing in the U.S., including a favorable true-up to customer discounts, partially offset by lower demand in China, ongoing generic competition in most other international markets, and continuing volume declines in the U.S. due to competitive pressure.

The American Rescue Plan Act enacted in the U.S. in 2021 included a provision that eliminated the statutory cap on rebates drug manufacturers pay to Medicaid beginning in January 2024. As a result of this provision, the Company paid state Medicaid programs more in rebates than it received on Medicaid sales of Januvia, Janumet and Janumet XR in 2024. In early 2025, Merck lowered the list price of the Januvia family of products to more closely align them with net prices. The lower list price has reduced the rebate amount Merck pays to Medicaid, resulting in higher realized net pricing.

While the key U.S. patent for Januvia, Janumet and Janumet XR claiming the sitagliptin compound expired in January 2023, as a result of favorable court rulings and settlement agreements related to a later expiring patent directed to the specific sitagliptin salt form of the products, the Company expects that Januvia and Janumet will not lose market exclusivity in the U.S. until May 2026 and Janumet XR will not lose market exclusivity in the U.S. until July 2026, although a non-automatically substitutable form of sitagliptin that differs from the form in the Company’s sitagliptin products has been approved by the FDA. Additionally, HHS, through the CMS, selected Januvia

59

Table of Contents

in 2023 for the first year of the IRA’s Program, and selected Janumet and Janumet XR in 2025 for the second year of the IRA’s Program. Pursuant to the IRA’s Program, the government set a price for Januvia, which became effective on January 1, 2026, and set a price for Janumet and Janumet XR, which will become effective on January 1, 2027. The Company has sued the U.S. government regarding the IRA’s Program. See Note 10 to the consolidated financial statements for additional information related to the above-referenced patent and IRA litigation. The Company expects a significant decline in sales of Januvia in the first half of 2026 reflecting the impact of government price setting noted above and subsequently, following loss of market exclusivity in May 2026, the Company anticipates it will lose nearly all U.S. sales of Januvia and Janumet.

Animal Health Segment

Sales of livestock products grew 13% in 2025 primarily due to increased demand across all species, the inclusion of sales from the July 2024 acquisition of the aqua business of Elanco Animal Health Incorporated (Elanco aqua business), improved supply, new product launches, and higher pricing. See Note 3 to the consolidated financial statements for additional information related to the acquisition of the Elanco aqua business.

Sales of companion animal products grew 2% in 2025 reflecting higher pricing, new product launches, and improved supply, partially offset by lower demand for other products in the portfolio. Sales of the Bravecto line of products were $1.1 billion in 2025, an increase of 1% compared with 2024.

In July 2025, the FDA approved Bravecto Quantum, a once-yearly injectable product to treat and protect dogs from fleas and ticks. Also in July 2025, the EC approved Numelvi tablets for dogs, a once-daily, second-generation Janus kinase (JAK) inhibitor indicated for the treatment of pruritus associated with allergic dermatitis including atopic dermatitis and treatment of clinical manifestations of atopic dermatitis.

Costs, Expenses and Other

Other (income) expense, net 151 * (24) * 466

* >100%

Cost of Sales

Cost of sales was $16.4 billion in 2025 and $15.2 billion in 2024. Cost of sales includes the amortization of intangible assets recorded in connection with acquisitions, collaborations, and licensing arrangements, which totaled $2.8 billion in 2025 and $2.4 billion in 2024. Additionally, cost of sales in 2025 includes an $83 million impact for the recognition of fair value step-up of inventories related to the Verona Pharma acquisition. Also included in cost of sales are expenses associated with restructuring activities, which amounted to $1.5 billion in 2025 and $495 million in 2024, primarily reflecting accelerated depreciation and asset impairment charges related to manufacturing facilities to be fully or partially closed or divested, as well as contractual termination costs. Separation costs associated with manufacturing-related headcount reductions have been incurred and are reflected in Restructuring costs as discussed below.

Gross margin was 74.8% in 2025 compared with 76.3% in 2024. The gross margin decline was primarily due to the negative impacts of higher restructuring costs (primarily related to the accelerated depreciation of manufacturing lines at two sites under the 2025 Restructuring Program), higher inventory write-downs (primarily vaccines), increased amortization of intangibles, and the recognition of fair value step-up of inventories related to the Verona Pharma acquisition, partially offset by the favorable impact of product mix.

60

Table of Contents

Selling, General and Administrative

Selling, general and administrative (SG&A) expenses were $10.7 billion in 2025, a decline of 1% compared with 2024. The decrease was primarily driven by lower restructuring and promotional costs, partially offset by increased administrative costs.

Research and Development

Research and development (R&D) expenses were $15.8 billion in 2025, a decline of 12% compared with 2024. The decline was primarily due to lower charges for business development activity.

Significant business development transactions in 2025 include charges of:

•$300 million for completion of the technology transfer for MK-2010 (LM-299) from LaNova Medicines Ltd (LaNova, acquired by Sino Biopharmaceutical Limited)

•$200 million for a license agreement with Hengrui Pharma

•$150 million related to an agreement with Falk to acquire sole global rights to MK-8690

•$100 million for the achievement of a developmental milestone related to the 2024 Eyebiotech Limited (EyeBio) acquisition

Significant business development transactions in 2024 include charges of:

•$1.35 billion for the acquisition of EyeBio and $100 million for the achievement of a related developmental milestone

•$750 million for the acquisition of MK-1045 (formerly CN201) from Curon Biopharmaceutical

•$656 million for the acquisition of Harpoon Therapeutics, Inc. (Harpoon)

•$588 million for a global license agreement with LaNova

•$112 million for a global license agreement with Hansoh Pharma (Hansoh)

The decline in R&D expenses was partially offset by higher clinical development spending, higher restructuring costs, and increased investment in discovery research and early drug development.

R&D expenses consist of the costs directly incurred by Merck Research Laboratories (MRL), the Company’s research and development division that focuses on human health-related activities, which were $10.8 billion in 2025 and $10.1 billion in 2024. Also included in R&D expenses are Animal Health research costs, upfront and milestone payments for collaboration and licensing agreements (including charges related to the transactions with LaNova, Hengrui Pharma, Falk, and Hansoh noted above), charges for transactions accounted for as asset acquisitions (including charges for the acquisitions of EyeBio, MK-1045, and Harpoon noted above), and costs incurred by other divisions in support of R&D activities, including depreciation, production, and general and administrative, which in the aggregate were $4.8 billion in 2025 and $7.7 billion in 2024. R&D expenses also include restructuring costs of $175 million in 2025 associated with contractual termination costs.

Restructuring Costs

In July 2025, the Company approved a new restructuring program (2025 Restructuring Program) designed to position the Company for its next chapter of growth and to successfully advance its pipeline and launch new products across multiple therapeutic areas. As part of this program, the Company expects to eliminate certain positions in sales and administrative organizations, as well as research and development. The Company will, however, continue to hire employees into new roles across all strategic growth areas of the business. In addition, the Company will reduce its global real estate footprint and continue to optimize its manufacturing network, aligning the geography of its global manufacturing footprint to its customers and reflecting changes in the Company’s business. Most actions contemplated under the 2025 Restructuring Program are expected to be largely completed by the end of 2027, with the exception of certain manufacturing actions, which are expected to be substantially completed by the end of 2029. The cumulative pretax costs to be incurred by the Company to implement the program are estimated to be approximately $3.0 billion, of which approximately 60% will be cash, relating primarily to employee separation expense and contractual termination costs. The remainder of the costs will be non-cash, relating primarily to the accelerated depreciation of facilities. The Company expects the actions under the 2025 Restructuring Program to result in annual cost savings of approximately $1.7 billion, which will be substantially realized by the end of 2027. The 2025 Restructuring Program is part of the Company’s multiyear optimization initiative anticipated to achieve $3.0 billion in annual cost savings by the end of 2027, which will be fully reinvested into strategic growth areas of the business.

61

Table of Contents

In January 2024, the Company approved a restructuring program (2024 Restructuring Program) intended to continue the optimization of the Company’s Human Health global manufacturing network as the future pipeline shifts to new modalities and also optimize the Animal Health global manufacturing network to improve supply reliability and increase efficiency. The actions contemplated under the 2024 Restructuring Program are expected to be substantially completed by the end of 2031, with the cumulative pretax costs to be incurred by the Company to implement the program estimated to be approximately $4.0 billion. Approximately 50% of the cumulative pretax costs will be non-cash, relating primarily to the accelerated depreciation of facilities to be closed or divested. The remainder of the costs will result in cash outlays, relating primarily to facility shut-down costs. The Company anticipates the actions under the 2024 Restructuring Program will result in cumulative annual net cost savings of approximately $750 million by the end of 2031.

Restructuring costs of $889 million in 2025 and $309 million in 2024 primarily include separation and other costs associated with these restructuring activities. Separation costs incurred were associated with actual headcount reductions, as well as estimated expenses under existing severance programs for involuntary headcount reductions that were probable and could be reasonably estimated. Other expenses in Restructuring costs include facility shut-down and other related costs, as well as employee-related costs such as curtailment, settlement, and termination charges associated with pension and other postretirement benefit plans, and share-based compensation plan costs. For segment reporting, restructuring costs are unallocated expenses.

Additional costs associated with the Company’s restructuring activities are included in Cost of sales, Selling, general and administrative expenses and Research and development costs. The Company recorded aggregate pretax costs related to restructuring program activities of $2.6 billion in 2025 and $888 million in 2024. See Note 5 to the consolidated financial statements for additional details.

Other (Income) Expense, Net

Other (income) expense, net, was $151 million of expense in 2025 compared with $24 million of income in 2024. The unfavorable year-over-year change primarily reflects $170 million of income in 2024 related to the expansion of an existing development and commercialization agreement with Daiichi Sankyo, as well as higher net interest expense and higher foreign exchange losses in 2025, partially offset by higher net income from investments in equity securities in 2025.

For details on the components of Other (income) expense, net, see Note 14 to the consolidated financial statements.

Segment Profits

Pharmaceutical segment profits consist of segment sales less standard costs, as well as SG&A expenses directly incurred by the segment. Animal Health segment profits consist of segment sales, less all cost of sales, as well as SG&A and R&D expenses directly incurred by the segment. For internal management reporting presented to the chief operating decision maker, Merck does not allocate the remaining cost of sales not included in segment profits as described above, R&D expenses incurred by MRL, or general and administrative expenses not directly incurred by the segments, nor the cost of financing these activities. Separate divisions maintain responsibility for monitoring and managing these costs, including depreciation related to fixed assets utilized by these divisions and, therefore, they are not included in segment profits. Also excluded from the determination of segment profits are costs related to restructuring activities and acquisition- and divestiture-related costs, including the amortization of intangible assets and the recognition of fair value step-up of inventories, intangible asset impairment charges, and expense or income related to changes in the estimated fair value measurement of liabilities for contingent consideration. Additionally, segment profits do not reflect other expenses from corporate and manufacturing cost centers and other miscellaneous income or expense. These unallocated items are reflected in “Non-segment activity” in the above table. Also included in “Non-segment activity” are miscellaneous corporate profits (losses), as well as operating profits (losses) related to third-party manufacturing arrangements.

62

Table of Contents

Taxes on Income

The effective income tax rate of 13.3% in 2025 reflects the favorable impacts of jurisdictional mix of income and expense, as well as certain discrete items.

The effective income tax rate of 14.1% in 2024 reflects a favorable jurisdictional mix of income and expense, as well as a 2.6 percentage point favorable impact due to a $519 million reduction in reserves for unrecognized income tax benefits resulting from the expiration in 2024 of the statute of limitations for assessments related to the 2019 and 2020 federal tax return years. The effective income tax rate in 2024 also reflects a 1.5 percentage point combined unfavorable impact of charges for the acquisition of Harpoon, for which no tax benefit was recognized, and the acquisitions of EyeBio and MK-1045 for which minimal tax benefits were realized.