Biogen Removed From Nasdaq-100; ETF Selloff Looms

Biogen Removed From Nasdaq‑100; ETF Selloff Looms

Biogen (BIIB) faces a near-term structural headwind: the company will be removed from the Nasdaq‑100 effective before the opening bell on December 22, 2025. That index exit, combined with elevated trading volumes and mixed technical signals, creates a clear set of risks and potential opportunities for investors positioned in the stock.

Index Exit and Immediate Market Impact

Index reconstitution is the driver: when the Nasdaq‑100 drops a name, ETFs and funds that track the index—most notably large passive products—must sell the stock. That mechanical selling typically increases supply over a concentrated window and can depress prices even when a company’s fundamentals remain unchanged.

For Biogen, the removal reflects recent visibility and liquidity criteria rather than therapeutic or pipeline news. The practical result is a predictable near-term seller: passive flows that will likely continue into the December 22 effective date. Think of it as a scheduled tide that temporarily lowers the waterline around all boats tied to the index.

Share Performance and Technical Signals

Recent Price Action

Biogen showed signs of investor caution in the last two weeks. On December 11 the stock declined roughly 2.8% to about $172.50 with volume near 2.7 million shares—well above its 50‑day average. On December 16 it fell another ~2.4% to roughly $171.50 with similarly elevated turnover. These moves underline near‑term selling pressure and investor repositioning ahead of the index change.

Momentum Metrics

Counterbalancing the supply pressure, technical momentum has improved: Biogen’s Relative Strength rating climbed into the mid‑80s, indicating the stock has outperformed a large portion of the market in recent weeks. That suggests buyer interest still exists, though some analysts note the stock has already moved beyond common short‑term entry thresholds—meaning disciplined investors may wait for consolidation or a pullback.

Fundamental Catalyst: Reduced Alzheimer’s Competition

On the fundamentals side, a significant development removed a competitive overhang: a rival Alzheimer’s candidate from Novo Nordisk failed in Phase 3, narrowing near‑term competitive risk for Biogen’s Leqembi. That outcome improves Biogen’s positioning in the small set of authorized disease‑modifying Alzheimer’s treatments and supports a more constructive medium‑term revenue narrative—an important counterweight to index‑related selling.

What This Means for Investors

• Expect heightened selling pressure from passive funds into the December 22 effective date; watch daily volume for signs of absorption.
• Short‑term volatility may create tactical buying opportunities for disciplined investors who prioritize fundamentals (e.g., Leqembi uptake) and can tolerate near‑term liquidity shifts.
• Loss of Nasdaq‑100 membership can reduce passive institutional demand and slightly increase the company’s cost of capital, but it does not change clinical or commercial progress.
• Monitor upcoming earnings commentary, prescription uptake metrics for Leqembi, and any additional index adjustments that could influence flow dynamics.

Conclusion

Biogen’s impending removal from the Nasdaq‑100 creates a clear, time‑bound pressure point that could depress the stock in the short term as passive funds divest. At the same time, improving technical momentum and a diminished competitive threat in Alzheimer’s therapy provide constructive counterarguments for longer‑term investors. The balance between mechanical selling and underlying fundamentals will determine whether the near‑term dip becomes an entry point or a longer correction.