Merck's Pipeline Is Worth More Than the Keytruda Cliff Suggests

Understanding the bull case requires appreciating what Keytruda has built. Revenue has grown from $48.7 billion in 2021 to $65 billion in 2025, a 33% increase driven primarily by Keytruda's expansion across indications. The drug is now approved in over 40 tumour types and combinations, making it the world's best-selling pharmaceutical product.

But the more important story is margin expansion. Gross margins have expanded from 72% in 2021 to approximately 81.5% as Keytruda has scaled. Operating income has doubled from $13.2 billion to $26.8 billion. The profit margin of 28.1% ranks among the highest in large-cap pharmaceuticals. This margin profile reflects Keytruda's pricing power and the operating leverage of a product with essentially fixed manufacturing costs at scale.

The 2023 anomaly, when net income collapsed to $365 million on what would have been a $17 billion year, was entirely due to the $10.2 billion charge related to the Prometheus Biosciences acquisition. Strip out that one-time charge and the underlying earnings power has grown consistently. The market sometimes forgets this: that 2023 dip in net income was an acquisition accounting event, not an operating deterioration.

The most underappreciated asset in Merck's portfolio is not a new drug. It is a new formulation of an existing one. Keytruda is currently administered intravenously, requiring patients to visit infusion centres for 30-minute sessions every three to six weeks. The subcutaneous formulation, which Merck has been developing with partner Kelun-Biotech, would allow injection in minutes, potentially in a physician's office or even at home.

Why does this matter for the patent cliff? Because the subcutaneous formulation carries its own patent protection, extending effective exclusivity well beyond the 2028 IV formulation expiry. Biosimilar manufacturers can replicate the IV version, but they cannot use the subcutaneous delivery technology without infringing Merck's new patents.

The precedent is Roche's Herceptin. When the IV formulation lost exclusivity, Roche launched a subcutaneous version (Herceptin Hylecta) that retained over 50% of the franchise revenue despite biosimilar competition. Physicians and patients preferred the convenience. Merck's subcutaneous Keytruda should achieve similar or better retention because the convenience advantage is even more pronounced for a drug administered as frequently as Keytruda.

The consensus models assume 50-60% revenue erosion for Keytruda by 2030. If subcutaneous conversion retains 50-60% of the franchise, the actual erosion is closer to 25-35%. That difference, on a $25 billion revenue base, is worth $3.5 to $6 billion in annual revenue, or roughly $30 to $50 per share in present value.

Winrevair (sotatercept), acquired through the Acceleron Pharma deal in 2021, is Merck's biggest pipeline asset outside of Keytruda. The drug was approved for pulmonary arterial hypertension (PAH) in March 2024 and is ramping rapidly. Peak revenue estimates range from $5 billion to $8 billion, which would make it one of the largest specialty drug launches in recent history.

The PAH market has been underserved for decades. Existing treatments manage symptoms but do not address the underlying vascular remodelling that drives disease progression. Winrevair works through a different mechanism (activin signalling), offering disease-modifying potential. Early commercial data suggests uptake is tracking ahead of the most optimistic launch models, with physicians rapidly adopting the drug as a first-line addition to existing therapy.

Beyond Winrevair, Merck's pipeline includes multiple Phase III assets: MK-2870 (an ADC for ovarian cancer), MK-4830 (anti-ILT4 for solid tumours), and the expanding Keytruda combination portfolio. The pipeline probability-adjusted value, using standard biotech methodology, adds an estimated $25 to $40 per share beyond the base business.

The bears argue that no pipeline can replace a $25 billion drug. Historically, that has been true for most companies. But Merck has something most pharma companies lack: a patent extension strategy (subcutaneous Keytruda) combined with a potential mega-blockbuster (Winrevair) combined with a deep combination trial portfolio. The probability that total pipeline value exceeds the Keytruda cliff is higher than the 16.7x PE implies.

Merck generated $12.4 billion in free cash flow in 2025 and $18.1 billion the year before. The variability reflects the timing of large milestone payments and working capital movements, but the underlying cash generation capacity is enormous. With $14.6 billion in cash on the balance sheet, Merck has the financial flexibility to fund both organic pipeline development and strategic acquisitions without compromising the dividend.

The dividend yield has not been disclosed in the screener data, but at the current payout rate, Merck returns approximately $7 to $8 billion annually to shareholders through dividends and buybacks. The payout ratio is well below 50% of free cash flow, leaving substantial room for special dividends or accelerated buybacks as the Keytruda transition approaches.

Management's capital allocation during the transition period will be critical. The Prometheus acquisition in 2023 ($10.8 billion) demonstrated willingness to pay for growth. If Merck deploys $15 to $20 billion in bolt-on acquisitions over the next three years, targeting late-stage oncology and immunology assets, the post-cliff revenue gap narrows further.