Alnylam Stock Plunges 19%: Amvuttra Sales Jump 65% — and Investors Sold Anyway

Alnylam Pharmaceuticals (NASDAQ: ALNY) shares plunged about 19% on Thursday, October 29, 2026, trading near $188.23 from a prior close of $232.40, even though the biotech beat revenue expectations and its flagship drug Amvuttra grew sales 65%. The sell-off was not about the headline quarter investors just got — it was about the growth pace they now expect next, after management guided full-year TTR sales toward the low end of its range and flagged slower U.S. demand conversion.

What happened

Alnylam reported third-quarter 2026 results on Thursday morning. Total revenue rose 17% year over year to $1.458 billion, above a market estimate of about $1.43 billion. Net product revenue jumped 52% to $1.292 billion, driven almost entirely by the company's transthyretin amyloidosis (TTR) franchise.

Amvuttra (vutrisiran) generated $1.130 billion in the quarter, up 65% from a year earlier. Total TTR product revenue reached $1.150 billion, up 59%, while the smaller Rare portfolio added $142.0 million, up 12%. Royalty revenue more than doubled to $94.7 million on higher Leqvio sales.

On the surface, that is a strong commercial quarter. The stock fell anyway — hard — in one of the day's largest declines among large healthcare names, cutting Alnylam's implied market value to roughly $25.2 billion.

Why the stock is plunging despite a revenue beat

The problem is momentum, not the reported number. Coverage of the earnings call pointed to slower U.S. growth for Amvuttra and Onpattro, and to management saying physician interest is converting into patient demand more slowly than hoped. Alnylam reiterated its full-year guidance, but indicated TTR product sales should land near the low end of the stated range — a signal investors read as softening momentum for the franchise that now supplies about 89% of product revenue.

Management also cited a headwind from more restrictive first-line Medicare Advantage access after a UnitedHealth policy change that took effect on October 1. For a launch-stage growth story priced on rapid uptake in ATTR cardiomyopathy, any friction in access or conversion matters more than a single quarter's beat.

Profit quality added to the caution. GAAP operating income fell 6% to $345.8 million as product costs, research spending and commercial launch costs rose, and collaboration revenue dropped 80% against a prior-year quarter that included a $300 million Roche milestone. Reported net income of $2.167 billion and GAAP earnings of $15.72 per share were flattered by a roughly $1.9 billion income-tax benefit, mainly from releasing valuation allowances on U.S. deferred tax assets — not by operating growth. At least one research firm also cut its rating on the stock the same day, with a $225 price target.

Key facts

• Stock move: Down about 19.01% to $188.23 in Thursday trading, from a $232.40 prior close.
• Total revenue: $1.458 billion, up 17% year over year and above the roughly $1.43 billion estimate.
• Amvuttra sales: $1.130 billion, up 65% year over year.
• Net product revenue: $1.292 billion, up 52%; total TTR revenue $1.150 billion, up 59%.
• Operating income: $345.8 million on a GAAP basis, down 6%, as costs rose faster than operating profit.
• Net income: $2.167 billion, including a roughly $1.9 billion tax benefit; GAAP EPS was $15.72.
• Guidance: Full-year 2026 outlook reiterated — total net product revenue of $4.7 billion to $5.1 billion, including TTR revenue of $4.2 billion to $4.5 billion — with TTR now expected near the low end.
• Cash: Cash, cash equivalents and marketable securities were $3.6 billion at quarter-end.

What's next

Investors will watch whether U.S. Amvuttra demand re-accelerates or whether the slower conversion management described becomes the new run rate. Pipeline news offers near-term catalysts either way: two-year HELIOS-B extension data are due at the American Heart Association meeting from November 6 to 9, and a U.S. decision on partnered cemdisiran is targeted for November 2026. Longer term, Alnylam enlarged its TRITON-CM Phase 3 study of nucresiran to about 2,250 patients from 1,750, while still pointing to a potential ATTR-CM launch by 2030 if results and approvals follow.

For now, Thursday's message from the market is clear: Alnylam delivered growth, but not the growth trajectory the share price had been counting on. This report describes what happened and why investors reacted; it is not a recommendation to buy, sell or hold any security.

Sources

TradingKey — Alnylam Q3 2026 earnings breakdown | Kalkine — Alnylam down 19% after Q3 results | Quiver Quantitative — softer Amvuttra momentum analysis | TradingView — Alnylam Q3 revenue and net income

FAQ

Why did Alnylam stock fall 19% after earnings?

Investors focused on slowing U.S. Amvuttra momentum, guidance for TTR sales near the low end of the range, and tighter Medicare Advantage access, rather than the quarter's revenue beat.

How much did Amvuttra sell in Q3 2026?

Amvuttra generated $1.130 billion in Q3 2026, up 65% year over year, out of Alnylam's total revenue of $1.458 billion.

Did Alnylam cut its 2026 guidance?

No. Alnylam reiterated its full-year outlook, including total net product revenue of $4.7 billion to $5.1 billion, but said TTR sales should land near the low end.

Why was Alnylam's net income so high?

Net income of $2.167 billion included a roughly $1.9 billion income-tax benefit from releasing valuation allowances on U.S. deferred tax assets, while GAAP operating income actually fell 6%.