Pfizer's experimental monthly weight-loss drug showed up to 12.3% weight loss in trials, with mild side effects and no plateau, but shares dropped due to a 10% discontinuation rate.

Pfizer's experimental monthly GLP-1 drug, PF-3944, achieved up to 12.3% weight loss over 28 weeks in a mid-stage trial, with no plateau and generally mild side effects, according to data released on February 3, 2026. The drug, acquired through a $10 billion purchase of Metsera, is part of Pfizer's push into the $150 billion obesity market, with 10 Phase 3 trials planned for 2026 and potential approval by 2028. Despite strong fourth-quarter earnings and sales, Pfizer's stock fell 3.5% on concerns about a 10% discontinuation rate due to side effects, though no severe gastrointestinal events were reported. Despite patent expiration and pricing pressures, the company reaffirmed its revenue forecast for 2026.