The Keytruda Cliff Is Real. Merck's Stock Has Already Priced the Fix.

Keytruda is the best-selling prescription medicine in the world and roughly half of Merck's revenue. Its core U.S. patent expires in 2028, which puts more than $25 billion of annual sales directly in front of biosimilar competitors. That is the loss-of-exclusivity event behind all the talk of Merck "banking on" new drugs to replace it — and the reason a patient investor should understand the timeline before worrying.

Here is the part that usually trips people up: the cliff is real, but it is not next quarter. In the first quarter of 2026, Keytruda sales grew 12% year over year to $8 billion, still the engine of everything else. The pain point is roughly two and a half years out, when biosimilars can enter the U.S. market. What happens in between — and what the stock has already done while you waited — is where the actual investment question sits.

The two years Merck has left

Merck reports the transition in its numbers today, not just in its press releases. First-quarter sales rose 5% to $16.3 billion. Newer bets are compounding: Winrevair, the rare-lung-disease launch, grew 88% to $525 million, and the company is running more than twenty new product launches at once. Management has said it tripled its drug pipeline since 2021 and targets roughly $50 billion a year from new launches by the mid-2030s.

The cleverest piece of defense is a more convenient version of Keytruda itself. A subcutaneous formulation, approved in late 2025, delivers the same drug as an injection instead of an infusion. It cannot stop biosimilars from copying the molecule, but it gives patients and doctors a reason not to switch, and it carries its own patent protection. The idea is to blunt what would otherwise be a brutal step-down.

Merck also has the cash to absorb the blow rather than be wrecked by it. Over the trailing twelve months it generated roughly $16 billion of free cash flow, a margin above 20% of sales, and it has raised its dividend for fourteen straight years. That is the durability evidence: the company can fund a decade of transition and pay you to wait.

The catch is the price

Here is where the standard Merck story stops being a bargain. This is not a beaten-down name awaiting an expectation reset. The stock is up about 37% this year and roughly 75% over the past twelve months, sitting near $145 with a market capitalization around $356 billion. On next year's estimated earnings it trades near 19 times. The market is not still pricing the old, single-drug Merck — it has already moved far ahead and is paying for the new one.

That matters because normally I hunt for companies where the crowd is still pricing the old story while the numbers improve underneath. Merck is the mirror image: the numbers still favor Keytruda growing, but the shares have already re-rated in anticipation of a successful handoff. Nothing about the transition is guaranteed. Replacing the profit of the world's top-selling drug is historically one of the hardest jobs in pharma, and the promised multi-billion launches are a decade's worth of execution risk away. At this multiple, you are paying full price for that uncertain handoff, not getting it cheap.

What would prove the case wrong

Do not judge this business by the headline earnings number. Merck swung to a reported loss in the first quarter because it took a roughly $9 billion, or $3.62 a share, acquisition charge for Cidara, with another sizable one-time charge tied to Terns coming. Those are accounting noise, not operations failing — the underlying business was profitable before them. Follow operating cash flow instead.

The case genuinely breaks, though, if three things happen together after 2028: if biosimilar erosion proves far faster than the historical pattern for oncology drugs, if the new launches stall before they reach meaningful revenue, or if Keytruda loses share of new patients sooner than modeled. Watch whether Keytruda keeps growing through 2026 and 2027, and whether the launch book actually converts into profit rather than staying a list of press releases.

Merck is a fine company and a dependable dividend payer, and it has a sensible plan for a real problem. But the easy entry passed while the stock ran up. What is left is a quality compounder where the risk and reward now depend on a long, uncertain pipeline — a bet you should make with eyes open at this price, not a beaten-down reset waiting to be bought.