Alnylam Pharmaceuticals cuts sales guidance amid Amvuttra performance issues

Alnylam Pharmaceuticals has experienced a significant decline in share value, losing more than half its value over the past 12 months and dropping over 20% in the last four weeks. The downturn follows disappointing sales for its transthyretin-mediated (ATTR) amyloidosis therapy, Amvuttra.

In its 2026 second-quarter results, the company lowered its full-year sales guidance for TTR products, including Amvuttra and Onpattro, by $200 million. CEO Yvonne Greenstreet attributed the reduced guidance to a better understanding of the ATTR-CM market, noting that previous strong growth benefited from pent-up demand that has since normalized.

Competition is increasing in the sector, as BridgeBio’s ATTR-CM drug, Attruby, reported sales that more than tripled year-over-year to $222.4 million in Q2. Additionally, uncertainty remains regarding Alnylam’s next-generation ATTR therapy, nucresiran, which is currently in late-stage clinical testing.