What impact will this new dosing regimen have on Biogen's revenue forecasts and market share compared to competing Alzheimer’s therapies such as Aduhelm and donanemab?

Revenue outlook: The FDA’s clearance of a weekly sub‑cutaneous (SC) maintenance dose removes a major barrier to patient adherence and payer acceptance. Compared with the original monthly IV infusion, the SC route cuts infusion‑center costs, shortens clinic time and opens the drug to a broader community‑practice setting. Analysts are likely to lift Biogen’s 2025‑2027 revenue guidance for Leqembi by roughly 10‑15 % (≈ $300‑$450 m of incremental sales) as the company can now capture a larger share of the early‑AD market that previously drifted to “no‑therapy” or off‑label options. The upgraded forecast should flow through to FY2025 EPS, pushing the consensus target price up 6‑9 % on the current level.

Market‑share dynamics: Leqembi already enjoys a pricing advantage (≈ $24,000‑$28,000 per patient per year) over Eli Lilly’s Aduhelm ($≈ 56,000) and is now positioned competitively against donanemab, which is priced similarly to Aduhelm but still pending full commercial rollout. The SC regimen shortens the “time‑to‑reimbursement” cycle, which should accelerate market penetration, especially in the Medicare Advantage and private‑insurer segments that have been cautious about monthly IV logistics. Assuming a modest 5‑7 % conversion of the 2‑3 m eligible early‑AD patients currently on Aduhelm or awaiting donanemab, Leqembi could command 30‑35 % of the U.S. early‑AD market by 2027, up from the ~22 % share reported in Q2 2025.

Trading implications: The news is already baked into the 75 % positive sentiment, but the upside to Biogen’s valuation still appears under‑priced. A short‑to‑mid‑term entry at current levels (≈ $220‑$225) with a target of $245‑$255 captures both the revenue lift and the relative market‑share gain versus Aduhelm/donanemab. Keep an eye on any CMS policy updates on SC administration and on Eli Lilly’s rollout timeline for donanemab—delays or pricing pressure there would further amplify Leqembi’s upside. A stop‑loss around $210 protects against a potential FDA‑related safety surprise, while a break‑out above $260 could signal the market pricing in a full‑year “best‑in‑class” positioning for Leqembi.