What Happens To Merck Stock If Keytruda Sales Stop Growing?

Shares of Merck (MRK) returned 76.2% over the past year, compared with 17.4% for the S&P 500. U.S. growth for the company’s cancer drug Keytruda is set to slow. Management said on the August 4 call that U.S. Keytruda growth will moderate as the drug reaches peak penetration across several key indications. Barron’s also reported on October 7 that a Dutch court barred Merck from selling subcutaneous Keytruda in eight European markets. So how much of what Merck sells is Keytruda?

How Much Of Merck’s Sales Come From Keytruda?

The answer is about half. The Keytruda family, which includes Keytruda QLEX, generated $8.4 billion in fiscal Q2 2026, compared with $16.6 billion of revenue for the whole company. Excluding currency, sales for the family grew 4% in that quarter, the same pace as total revenue on that basis.

That makes a Keytruda stall mainly a question about how fast Merck grows, and less about how big it is. The longer question centers on the period when Keytruda loses its market exclusivity. This timeline came up on the August call, when an analyst asked about the period from 2028 through the early 2030s. Management said it sees that period as “more of a hill than a cliff” and expects a shallow dip followed by a quick return to growth. Both the shallow dip and the quick recovery are management forecasts.

What Merck Has Besides Keytruda

Merck has several newer drugs growing much faster than Keytruda. WINREVAIR, for adults with pulmonary arterial hypertension, posted sales of $588 million in fiscal Q2 2026, up 75%. WELIREG sales rose 67% in the same quarter. Outside its human medicines, Animal Health operates as a separate reported segment. It recorded $6.35 billion of revenue in full-year 2025, up 8.1%, the latest year of segment figures.

Merck’s cash also paid its dividend about twice over in the twelve months to June 30, 2026. Free cash flow for the period reached $16.1 billion, compared with $8.3 billion of dividends paid. Management said on the August call that it remains committed to the dividend.

Debt is the weaker side. Total debt stood at $53.9 billion on June 30, 2026, rising from $35.4 billion a year earlier. Operating income still covered interest expense 4.0 times over the past twelve months.

When Will Merck Show Whether Keytruda Is Slowing?

Before its next report, Merck will host an investor event on the evening of Monday, October 26, at the European Society for Medical Oncology in Madrid. Management has also said the unwind of specialty pharmacy purchases made in the second quarter will affect third quarter sales.

Management’s own forecast is slower U.S. growth for Keytruda, not a stall. Keytruda family sales growth, 4% in fiscal Q2 2026, is the number to watch in the report Merck is expected to release on October 29.

Does This Mean You Should Act On MRK?

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