Why Alnylam Pharmaceuticals Stock Tumbled 28% Today

Shares of Alnylam Pharmaceuticals (NASDAQ: ALNY) plunged as much as 29% on Thursday, July 30, 2026, closing down roughly 27.8% at $206.88, after the RNAi therapeutics company reported second-quarter results that fell short of Wall Street’s lofty expectations and lowered its full-year outlook.

The selloff centered on disappointing sales of Amvuttra, Alnylam’s flagship treatment for transthyretin amyloidosis (ATTR). While the drug crossed $1 billion in quarterly revenue for the first time, its $1.01 billion haul missed analyst estimates by roughly 4%, with U.S. sales of $809 million coming in about 2% below consensus. Investors had grown accustomed to Amvuttra topping projections since its FDA approval for ATTR-cardiomyopathy in March 2025, making the miss especially jarring.

In response, Alnylam cut its full-year ATTR revenue guidance to a range of $4.2 billion to $4.5 billion, a $200 million reduction at both ends of the prior forecast. CEO Yvonne Greenstreet attributed the slowdown to normalizing second-line demand following a surge fueled by pent-up patient need after last year’s launch, while insisting the company’s “confidence in Amvuttra’s growth trajectory has never been stronger.”

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Executives, including Chief Commercial Officer Tolga Tanguler, spent much of Thursday’s investor call defending the drug’s long-term trajectory, citing strong physician adoption, adherence above 90%, and accelerating U.S. demand growth quarter-over-quarter. Roughly 80% of new ATTR-CM starts are first-line treatments — the segment Alnylam is prioritizing as competitors Pfizer and AstraZeneca/Ionis navigate their own setbacks in the space.

Despite the guidance cut, Alnylam posted GAAP net income of $164.5 million for the quarter, swinging from a year-ago loss, with net product revenue up 74%. The company also highlighted new clinical trials targeting bleeding disorders and Alzheimer’s disease. Still, investors focused squarely on the guidance reduction, sending shares to their worst single-day performance in recent memory.