Insmed Stock (NASDAQ: INSM) Slides on Brensocatib Sinus-Trial Failure; Analysts Reset Forecasts
December 18, 2025 — Insmed Incorporated (NASDAQ: INSM) shares dropped sharply Thursday after the company disclosed a Phase 2b setback for brensocatib in a chronic sinus condition and said it is discontinuing development in that indication, even as it simultaneously added a new Phase 2–ready antibody to its pipeline. SEC+1 Insmed stock was trading around $166.75 in the afternoon snapshot available from market data, down about 16% on the day, after touching an intraday low of $158.06 and high of $173.99. What happened to INSM stock on December 18, 2025 The selloff traces back to Insmed’s disclosure that its Phase