Leqembi Momentum Stalls; Biogen Downgrade Reflects Growth Transition Doubts

What happened

Biogen's shares have been downgraded by Seeking Alpha, as the analyst argues that accelerating Leqembi sales are still insufficient to offset the structural decline in the multiple sclerosis franchise and prevent overall revenue stagnation. The DeepValue report maintains a WAIT rating with a $183.79 price, reflecting modest upside potential but emphasizing that the stock already prices in revenue stabilization, leaving little room for error. While Q3 2025 launch products grew 67% year-over-year and rare-disease revenue expanded 8%, these gains are being offset by persistent MS erosion and repeated EPS guidance cuts from business-development charges. The company's transition toward Alzheimer's and rare neurology is real and progressing, but Leqembi's safety monitoring hurdles and the time required for new launches to reach critical mass mean near-term growth remains elusive. The market's current valuation of ~16.8x earnings offers a reasonable entry only if 2026 guidance confirms at least 3% revenue growth and sustained launch product acceleration; otherwise, downside toward the $160 bear case is possible.

Implication

The downgrade and ongoing transition underscore the need for patience; investors should seek confirmation from 2026 guidance that rare-disease and Alzheimer's growth can sustainably offset MS declines, with a re-assessment window of 6-12 months. The $165 attractive entry provides a margin of safety for patient capital, but the stock may trade sideways until clearer growth signals emerge.

Thesis delta

The narrative shifts from 'Leqembi is gaining traction and will stabilize revenue' to 'Leqembi's progress, while real, is insufficient to overcome MS headwinds and BD-related earnings drags, pushing the stock into a wait-and-see pattern.' This is consistent with the WAIT rating but with increased emphasis on the risk of revenue stagnation persisting through 2026.