Merck & Co. delivered fourth-quarter 2025 results that, on the surface, looked like a win. Adjusted earnings of $2.04 per share edged past consensus. Revenue hit $16.4 billion, up 5% year-over-year. But beneath the headline, a quietly unsettling picture is forming — one that the company's own 2026 guidance is only beginning to expose.
The $3.65 Charge That Changes Everything
Merck's 2026 adjusted EPS guidance of $5.00–$5.15 initially alarmed Wall Street. The reason is buried in the math: a one-time charge of approximately $3.65 per share tied to its $9.2 billion acquisition of Cidara Therapeutics, a biotech developing a long-acting flu prevention antiviral called CD388. Strip out that charge, and "normalized" 2026 EPS lands around $8.65–$8.80. That number sounds manageable — until you compare it to Merck's full-year 2025 EPS of $8.98. The implication is stark: despite billions deployed on acquisitions, the company's underlying earnings power is contracting by roughly 3% year-over-year. The deals are plugging holes, not filling them.
Keytruda: Still the Empire, But the Walls Are Thinning
Keytruda, Merck's cancer immunotherapy and the single largest revenue engine in global pharmaceuticals, posted $8.37 billion in quarterly sales — up 7% annually and ahead of estimates. But context matters. A year prior, Keytruda grew 21% in the same quarter. The deceleration is not cosmetic; it reflects a franchise entering its mature phase ahead of a 2028 patent expiration that threatens to erase nearly $25 billion in annual revenue as biosimilars flood the market.
Merck's counter-move is Keytruda QLEX, a subcutaneous formulation approved by the FDA in September 2025. It recorded $35 million in Q4 sales — a start, but not a salvation. QLEX is fundamentally a defensive asset: it extends the brand's commercial life by offering patients a faster, more convenient injection. It does not create new demand. The real battleground will be payer formularies, where the calculus flips the moment a cheaper biosimilar becomes available. Bristol Myers Squibb's Opdivo Qvantig, a direct subcutaneous competitor, was already approved in late 2024.
Gardasil and Enflonsia: Two Stumbles That Deserve More Attention
Two products buried deeper in Merck's earnings reveal commercial vulnerabilities the market has not fully priced. Gardasil, the HPV vaccine that was once a reliable high-margin growth engine, saw sales plummet 35% in Q4 to $1.03 billion. The primary culprit is China, where a domestic 9-valent HPV competitor has entered at deep discounts, structurally resetting the market. Compounding the problem, the CDC shifted to a one-dose HPV recommendation in late January 2026, which could mechanically reduce U.S. volume over time. Gardasil is no longer a second pillar — it is now a risk factor.
Then there is Enflonsia, Merck's RSV immunization product, which posted just $21 million in sales. The company acknowledged "high levels of total RSV mAb inventory in the market" and took inventory write-offs that contributed to a quarter-point decline in gross margins. This is a textbook botched launch: production scaled for a blockbuster, demand never materialized. With Cidara representing another $9.2 billion bet on a seasonal respiratory franchise, investors are right to question Merck's ability to read these markets.
Winrevair, Cidara, and the Pipeline Gamble
Not everything is cautionary. Winrevair, a treatment for pulmonary arterial hypertension launched in mid-2024, delivered $467 million in Q4 — a 133% increase year-over-year. It is the most credible internal offset to the Keytruda cliff today, and its ramp trajectory warrants close watching through 2026.
Cidara is a higher-variance proposition. CD388 showed up to 76% efficacy in mid-stage trials against symptomatic flu over 24 weeks — promising data. But Merck paid a steep premium for a pre-revenue asset in a space where Enflonsia just failed commercially. The $9 billion question is whether CD388 can achieve the broad, durable uptake its price tag demands. Late-stage pipeline assets — including an oral PCSK9 inhibitor and a TL1A inhibitor for ulcerative colitis — add optionality, but optionality does not close a $25 billion revenue gap on a timeline.
The Government Deal Nobody Is Talking About
Merck disclosed an agreement with the U.S. Department of Commerce that delays Section 232 tariffs on pharmaceutical imports for three years. The trade-off: a direct-to-patient affordability program that almost certainly includes pricing concessions on mature products. For investors, this is a gross-margin ceiling. Historical margin assumptions for the 2026–2028 window are likely too generous. It is a rational deal — supply-chain certainty in exchange for pricing flexibility — but it quietly caps the upside on the parts of the portfolio that are supposed to hold the line while Keytruda ages.
A Transition Year That Still Leaks
Merck is not in crisis. It holds a dominant oncology franchise, a fast-scaling asset in Winrevair, and multiple Phase 3 programs with genuine commercial potential. But the 2026 picture — flat-to-shrinking organic earnings, a wobbling Gardasil franchise, a high-risk respiratory bet, and a government-imposed pricing ceiling — does not yet tell the story of a company that has solved its post-Keytruda future. It tells the story of one that is still building the bridge while standing on it. Until QLEX demonstrably slows biosimilar share loss, Gardasil finds a durable floor, and Winrevair sustains its ramp without surprise, the most disciplined posture is cautious neutrality — and close attention to what 2026 actually delivers.
not investment advice!!!