Key Highlights

● Alnylam said TTR Franchise sales will likely land at the low end of guidance.

● Third-quarter total Revenue reached $1.46 billion, with U.S. Amvuttra sales of $909 million.

● Shares traded near $174.00 after being indicated near $192.38 before the open.

● Management said 2027 guidance will not arrive until February.

Alnylam Pharmaceuticals (NASDAQ:ALNY) grew sales briskly in the third quarter, but a cautious word on its most important franchise triggered a steep selloff on Thursday.

Strong growth, wrong message

On paper, Alnylam's third quarter looked impressive. The RNA-interference drug developer reported net product revenue of about $1.29 billion before the opening bell on October 29, a sharp increase from a year earlier. Total revenue reached $1.46 billion, and U.S. sales of Amvuttra, its flagship treatment, came in at $909 million.

The market zeroed in on something else. Alnylam said sales from its TTR franchise, which treats transthyretin amyloidosis, a disease in which misfolded proteins build up in the heart and nerves, would likely land at the low end of guidance.

The stock plunged, trading near $174.00 according to market data, after being indicated near $192.38 before the open. It was one of the worst performers in the Nasdaq-100.

Why Demand matters so much

Alnylam reiterated its 2026 product revenue guidance of $4.7 billion to $5.1 billion. But flagging the low end for TTR, the company's growth engine, was enough to reset expectations.

Management pointed to slower conversion of demand into prescriptions, uncertainty around the federal 340B drug pricing program, and access challenges within Medicare Advantage plans. One report noted that some of those plans may require patients to try other therapies before Amvuttra. Another source reported that management said Amvuttra demand would not accelerate in the fourth quarter.

Chief executive Yvonne Greenstreet was candid. The company is "not yet satisfied with the underlying demand growth we have observed," she said.

Margins and missing guidance

Profitability also moved the wrong way. Alnylam's non-GAAP operating Margin narrowed noticeably from the prior year. And the company said 2027 guidance would not arrive until February, leaving investors with less visibility just as they were reassessing the growth trajectory.

Reports differed on what weighed most. One emphasized the TTR guidance comment, while another focused on the outlook for Amvuttra demand in the fourth quarter. Both pointed to the same underlying worry: slower growth than investors had hoped.

A rare loser in a winning sector

Alnylam's plunge stood out because health care was the best-performing sector in the S&P 500 on Thursday. Eli Lilly (NYSE:LLY) closed at an all-time high of $1,373.70 after raising its revenue guidance, Merck (NYSE:MRK) beat and lifted its profit outlook, and Insmed (NASDAQ:INSM) soared on stronger-than-expected sales of its lung drug Brinsupri.

The contrast underlined how unforgiving this Earnings season has become. Investors are rewarding upside surprises with sharp gains and punishing any hint of slowing demand just as hard.

The broader market was split. The Nasdaq Composite tumbled 365.13 points to 26,184.72 as Alphabet (NASDAQ:GOOGL) suffered its worst day since its 2004 IPO, while the Russell 2000 climbed 28.71 points to 2,859.22 and more than 400 S&P 500 members rose.

Macro data kept rates in focus. Third-quarter GDP grew faster than expected, and September PCE Inflation ran hot, keeping traders leaning toward a December rate hike from the Federal Reserve.

What to watch

The key question for Alnylam is whether TTR demand picks up as the company works through the access issues it described. Any progress on Medicare Advantage coverage or clarity on the 340B program could change the narrative.

February's 2027 guidance now looms as the next major catalyst. In the meantime, investors will track weekly prescription trends and any updates from management at upcoming conferences. Broader health care sentiment will be tested Friday when AbbVie (NYSE:ABBV) reports, alongside the third-quarter Employment Cost index and the Fed's December 8 to 9 meeting ahead.