Alnylam (ALNY) Stock: Why It Fell 19% on Slower Amvuttra Demand

Quick answer

Alnylam fell 19.3% to $187.57 at 12:04pm ET on Oct 29, 2026, from a $232.40 close, after its management said the heart drug that drives the company is growing more slowly than planned. Third-quarter Amvuttra sales rose 65% to $1.130 billion but came in below the $1.15 billion analyst average, and on the 8:30am call CFO Jeff Poulton said 2026 TTR sales should land "at the low end of our 4.2 billion to 4.5 billion dollar range." He said efforts to widen the prescriber base "are not yet translating into demand at the pace that we anticipated," and that Alnylam will not give 2027 product guidance in January as it has in past years. The stock had traded up to $242.00 at 8am, before the call, and was at $185.00 by 9:25am. It set a 52-week low of $179.87 in the first minutes of the session, on volume that reached 4.4 million shares by 12:04pm, 3.1 times its 20-day average for a full day. The drop took about $6 billion off its market value.

Our view: Bearish through February 15, 2027, around when Alnylam plans to report fourth-quarter results and give its first 2027 guidance. The case for the stock: Amvuttra still grew 65%, Alnylam holds $3.6 billion of cash and marketable securities, the shares trade about 19 times forward earnings and far below the $347 average analyst target, and near-term news is mostly favorable, with two-year HELIOS-B data at the American Heart Association meeting on Nov 6 to 9 and a November FDA decision on Regeneron's cemdisiran. The case against carries more weight into February. The company itself is pointing to the bottom of a range it already cut once in July, a Medicare Advantage restriction on first-line use started Oct 1, a 340B rule change could make fourth-quarter orders volatile, and with no 2027 guide until February, 2027 revenue estimates can only drift down to meet the new pace. The second expansion of TRITON-CM adds doubt to the drug meant to extend the franchise. We would move off Bearish if fourth-quarter US demand growth beats the $81 million added in the third quarter, if TTR sales land above the low end of the range, or if the HELIOS-B extension data show a clear survival gain that lifts first-line use. This is a view on direction over that window, not a recommendation to trade the stock.

Alnylam daily closing price from Sep 14 to Oct 29, 2026, with the Oct 2 low, the Oct 28 close before results and the Oct 29 low marked

Key takeaways

Alnylam fell 19.3% to $187.57 at 12:04pm ET on Oct 29, 2026, from a $232.40 close, after its third-quarter report and call. It traded as high as $242.00 before the call, opened at $184.91 and set a 52-week low of $179.87 in the first minutes.
Amvuttra sales of $1.130 billion rose 65% but came in below the $1.15 billion analyst average, and the $99 million US gain from the second quarter included a $17 million inventory benefit and about $10 million of favorable pricing adjustments.
CFO Jeff Poulton said 2026 TTR sales should land at the low end of the $4.2 billion to $4.5 billion range, that new prescribers are not turning into demand as fast as expected, and that Alnylam will not give 2027 guidance in January.
Alnylam also enlarged its TRITON-CM trial of nucresiran for the second time this year, to about 2,250 patients, citing event rates that can reduce a study's power.
Our view is Bearish through February 15, 2027, around the fourth-quarter report and first 2027 guidance: demand is slowing while a Medicare Advantage restriction and a 340B rule change add risk to the fourth quarter.

Table of contents

Oct 29, 2026: a premarket gain reverses on the call
The numbers: growth that is slowing
The bull case: a profitable franchise at a lower price
The risks
What comes next

Oct 29, 2026: a premarket gain reverses on the call

Alnylam published its results at 8am ET. The first premarket trades at 4am were at $236.18, and the stock reached $242.00 by 8am, up 4.1%. It fell through the 8:30am call to $185.00 by 9:25am, opened the regular session at $184.91 and set its low of $179.87 in the first minutes, a new 52-week low. It recovered to $202.37 at 10:20am, then slipped back. At 12:04pm it was $187.57.

What happened:

The quarter. Total revenue was $1.458 billion, up 17%. Total TTR revenue was $1.150 billion, up 59%, and Rare revenue $142 million, up 12%. Non-GAAP EPS of $16.26 included a $1.9 billion tax benefit from releasing valuation allowances, which Alnylam kept in its non-GAAP results, 24/7 Wall St. noted.
Demand underneath. US TTR revenue rose $99 million from the second quarter, of which $81 million was demand, $17 million an inventory benefit and the rest net price, helped by about $10 million of favorable gross-to-net adjustments. Poulton said the inventory and gross-to-net items "are not measures of underlying demand."
Guidance. Alnylam reiterated its 2026 ranges, $4.2 billion to $4.5 billion for TTR and $4.7 billion to $5.1 billion for all products, but steered TTR to the low end. Poulton cited a "more restrictive first line" Medicare Advantage policy effective Oct 1 and said a 340B rule "could create Q4 ordering volatility."
TRITON-CM. Alnylam is raising enrollment in the Phase 3 nucresiran trial to about 2,250 patients from 1,750, after raising it from about 1,250 in the spring. Pushkal Garg, who leads research and development, said secular trends "do tend to reduce event rates, which can compromise study power."
The Street. Stifel downgraded the stock to Hold with a $225 target.

Other RNAi and heart-drug names rose, so this was Alnylam alone. From the Oct 28 close, at 12:04pm:

Stock or fund	Oct 28 close	Oct 29, 12:04pm	Change
BridgeBio (BBIO)	$70.82	$71.89	+1.5%
Arrowhead (ARWR)	$60.21	$61.05	+1.4%
iShares Biotechnology (IBB)	$216.35	$217.84	+0.7%
SPDR S&P Biotech (XBI)	$157.51	$158.37	+0.5%
Ionis (IONS)	$44.90	$44.93	+0.1%
Alnylam (ALNY)	$232.40	$187.57	-19.3%

BridgeBio, whose Attruby competes with Amvuttra in ATTR cardiomyopathy, rose. After the drop, RSI(14) stood at 27, the shares sat 21% below their 50-day average and 34% below their 200-day average, and the stock was 61% below its 52-week high of $482.73.

The numbers: growth that is slowing

Bar chart of Amvuttra net product revenue: $685 million in Q3 2025, about $1,010 million in Q2 2026, $1,130 million in Q3 2026 and the $1,150 million analyst average for Q3 2026

Amvuttra added about $120 million from the second quarter, and part of that was inventory and pricing rather than patients. This is the second quarter in a row it has come in under the analyst average: in July it sold $1.01 billion against about $1.05 billion expected, and Alnylam cut its TTR range from $4.4 billion to $4.7 billion to the current one, BioPharma Dive reported. The stock fell nearly 30% that day. Management said on the Oct 29 call that converting new prescribers into patient starts "is taking longer than we'd hoped," and that newer prescribers have fewer cardiomyopathy patients. Our explainers on why guidance changes move stocks and how estimate revisions follow cover why a guide pinned to the low end can weigh on a stock for months.

The bull case: a profitable franchise at a lower price

Still growing fast. Total net product revenue rose 52%, and international TTR sales rose $20 million from the second quarter on launches in Japan, Germany and Italy.
Cash and profit. Alnylam ended September with $3.6 billion of cash and marketable securities, up from $2.9 billion at the end of 2025, on operating cash flow.
Data on the way. Two-year HELIOS-B extension results come at the American Heart Association meeting on Nov 6 to 9, and Alnylam will present a comparison of vutrisiran with BridgeBio's acoramidis at a symposium on Nov 15 to 18. Early brezosiran data in Huntington's disease showed mean reductions of 60% to 64% in the target protein at the top dose, and a pivotal study is planned for 2027.

The risks

340B volume. Asked by Stifel's Paul Matteis whether the rule could cut volume and not just price, Poulton said, "there could be impact on volume, we don't know that yet."
Competition. Amvuttra competes with Pfizer's Vyndamax and BridgeBio's Attruby, and Alnylam's earlier guidance cut followed a failed trial of AstraZeneca and Ionis's eplontersen that raised questions about combination use.
No 2027 number until February. Poulton said, "We will therefore not be providing 2027 product revenue guidance at JP Morgan as in past years." Our guide to forward and trailing P/E explains why a forward multiple is only as good as the estimate under it.

What comes next

The AHA meeting on Nov 6 to 9 and the cemdisiran decision in November come first. The fourth-quarter report in mid-February will show whether TTR sales cleared the low end of the range and will carry the first 2027 guidance. Our guide to FDA decision dates covers how the cemdisiran date works, and more of the day's swings are in today's biggest stock moves.

Frequently asked questions

Why did Alnylam stock drop today?

Alnylam fell 19.3% to $187.57 at 12:04pm ET on Oct 29 after it said 2026 TTR sales should land at the low end of its $4.2 billion to $4.5 billion guidance. Amvuttra sales of $1.130 billion were below the $1.15 billion analysts expected, management said new prescribers are converting to patients more slowly than planned, and it expanded the TRITON-CM trial again.

Did Alnylam beat earnings?

On paper, yes. Non-GAAP EPS was $16.26, but that includes a $1.9 billion tax benefit from releasing valuation allowances on US deferred tax assets, which Alnylam did not exclude. Total revenue was $1.458 billion, up 17%, against an average estimate of about $1.45 billion. GAAP income from operations fell 6% to $345.8 million.

How much did Amvuttra sell in the third quarter?

Amvuttra net product revenue was $1.130 billion, up 65% from $685 million a year earlier, against an analyst average of $1.15 billion. Total TTR revenue, Amvuttra plus Onpattro, was $1.150 billion, up 59%. US TTR revenue rose $99 million from the second quarter: $81 million from demand, $17 million from inventory and a modest net price gain.

Why is Alnylam expanding the TRITON-CM trial?

Alnylam is raising target enrollment in the Phase 3 TRITON-CM study of nucresiran to about 2,250 patients from 1,750, after raising it from about 1,250 earlier this year. Pushkal Garg, who leads research and development, said secular trends tend to reduce event rates, which can compromise study power. Alnylam still expects a launch in ATTR cardiomyopathy by 2030 if the data are positive.

What did Stifel do on Alnylam?

Stifel downgraded Alnylam to Hold on Oct 29 and set a $225 price target. The average analyst target is about $347, far above the share price.

What are the next catalysts for Alnylam?

Alnylam presents two-year open-label data from the HELIOS-B trial at the American Heart Association meeting on Nov 6 to 9, and partner Regeneron has a November FDA decision date for cemdisiran in generalized myasthenia gravis, on which Alnylam would earn royalties of up to 15%. Fourth-quarter results and 2027 guidance are due in mid-February 2027.

Sources

Article details

By James Whitfield, Head of Equity Research, Dombey Capital

Published October 29, 2026 · 6 min read · Event-Driven Investing