Merck & Co. is still best known for Keytruda, but its next phase of growth will depend on how successfully it builds businesses beyond oncology.
For immunology and neurology, the company is investing in new medicines, acquisitions and late-stage clinical programs. The opportunity is significant, but so is the risk because these areas involve long clinical timelines, expensive trials and strong competition.
Merck’s Financial Strength Gives It Room to Invest
Merck generated $65.0 billion in worldwide sales in 2025, compared with $64.2 billion in 2024. Keytruda remained the largest contributor, generating $31.7 billion, up 7% from 2024.
The company is using this strong cash-generating base to expand into newer therapeutic areas. In 2025, Merck also saw strong growth from Winrevair, which reached $1.44 billion in sales, compared with $419 million in 2024.
This matters because Merck cannot depend on Keytruda indefinitely. The company needs additional growth products before the impact of future competitive pressure on Keytruda becomes more significant.
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Merck’s Key Financial Indicators
| Indicator | 2024 | 2025 |
|---|---|---|
| Total sales | $64.17B | $65.01B |
| Keytruda | $29.48B | $31.68B |
| Winrevair | $419M | $1.44B |
| Gardasil/Gardasil 9 | $8.58B | $5.23B |
| Lynparza alliance revenue | $1.31B | $1.45B |
| Lenvima alliance revenue | $1.01B | $1.05B |
Why Immunology Could Become an Important Growth Area
Merck’s immunology opportunity is being built around therapies that target specific inflammatory pathways rather than relying only on established treatments.
One important asset is tulisokibart, an investigational anti-TL1A antibody. Merck has been developing the medicine for inflammatory diseases, including ulcerative colitis and Crohn’s disease.
The opportunity is attractive because inflammatory bowel diseases require long-term treatment and patients may need multiple lines of therapy. A medicine that can demonstrate strong efficacy and a differentiated safety profile could become an important recurring-revenue product.
However, Merck has already seen how unpredictable this area can be. In 2026, tulisokibart produced a positive mid-stage result in hidradenitis suppurativa but failed a trial in a lung disease indication.
That mixed outcome shows why investors should evaluate individual clinical indications rather than assuming success across an entire therapeutic platform.
Neurology Could Open a Longer-Term Opportunity
Neurology represents a different type of opportunity for Merck.
The company has historically had exposure to neurological diseases, but its future growth strategy increasingly depends on finding medicines that can address large unmet needs while reducing dependence on its established franchises.
The company is also expanding its external innovation strategy through acquisitions and licensing. This approach is important in neurology because biotechnology companies often develop specialized assets that larger pharmaceutical companies can acquire after promising clinical data emerge.
Merck’s financial capacity allows it to take this approach. However, neurology programs typically require careful patient selection, long clinical trials and strong evidence that a biological target translates into meaningful patient benefit.
Where Is Merck Investing?
Merck is increasingly using acquisitions and business development to strengthen its pipeline.
In 2025 and 2026, the company made several significant transactions, including the acquisition of Terns Pharmaceuticals, which added the investigational oncology asset Ciforadenant, and the acquisition of Cidara Therapeutics, strengthening its infectious-disease portfolio.
In 2026, Merck also reported a $5.7 billion acquisition-related charge connected with Terns, showing that external innovation can require substantial capital before a product generates revenue.
For immunology and neurology, this creates an important strategic question: should Merck develop programs internally or acquire promising biotechnology companies after clinical validation?
The answer will depend on development stage, probability of technical success, competitive differentiation and expected commercial opportunity.
Demand and Growth Outlook
The underlying demand for immunology medicines remains supported by chronic inflammatory diseases that require long-term treatment.
Neurology offers another major opportunity because neurological disorders can create substantial long-term healthcare needs, particularly as populations age and diagnostic capabilities improve.
For Merck, the challenge is converting this demand into commercially successful medicines. A large patient population alone does not guarantee success.
The company needs medicines that offer measurable improvements in clinical outcomes, tolerability, convenience or durability compared with existing therapies.
What Should Leaders Look at Before Investing?
Leaders evaluating Merck’s immunology and neurology strategy should look beyond total company revenue.
First, examine pipeline quality. Look at Phase 2 and Phase 3 efficacy, safety, durability and probability of regulatory approval.
Second, evaluate competitive differentiation. A new medicine needs a clear reason for physicians to prescribe it instead of an established biologic or small molecule.
Third, watch acquisition spending. Merck has substantial financial capacity, but large acquisitions can create major upfront charges and integration risk. The Terns transaction illustrates this clearly.
Fourth, monitor revenue diversification. Keytruda generated about $31.7 billion in 2025, nearly half of Merck’s total sales. A successful investment should therefore help create meaningful revenue streams beyond oncology.
Finally, leaders should assess patent timelines, regulatory risk, trial design, reimbursement, manufacturing requirements and peak-sales potential before allocating capital.
Overall Growth Outlook
Merck has the financial strength to build a meaningful second wave of growth, but immunology and neurology are still developing pieces of the broader strategy.
The company enters this expansion from a powerful position: $65.0 billion in 2025 sales, $31.7 billion from Keytruda and rapidly growing products such as Winrevair.
The central question is whether Merck can convert its pipeline and external investments into several billion-dollar products before Keytruda faces greater competitive pressure.
For leaders and investors, the most important signals to watch are late-stage clinical success, new regulatory approvals, acquisition quality, pipeline diversification and the speed at which new products begin contributing meaningful sales.
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