Weight loss with GLP-1s is gradual and dose-dependent. STEP-1 (Wegovy 2.4 mg, NEJM 2021) showed mean body weight reduction of 5.9% at week 16, 13.5% at week 52, and 14.9% at week 68. SURMOUNT-1 (tirzepatide 15 mg, NEJM 2022) showed greater loss: 8% at week 16, 19% at week 52, 20.9% at week 72.
Individual variation is substantial. Roughly 30% of patients are "high responders" (>20% loss on Wegovy, >25% on Zepbound). Another 30% are "low responders" (<5% loss at 16 weeks) — for them, switching to tirzepatide or adding a non-GLP-1 agent is the typical next step.
Loss plateaus around month 14-18 on both drugs. The maintenance phase is the goal; weight regain begins within 4-8 weeks of discontinuation per STEP-4 and SURMOUNT-4 data.
The weight-loss estimator uses STEP/SURMOUNT trial data to project personalized loss curves based on starting BMI and target dose.