Average weight loss is one way to read a trial. Responder rate — the percentage of participants who actually crossed a clinically meaningful threshold — is often a more useful one. It tells you how often the medication "worked," not just how big the average was.
In STEP 1, the responder thresholds were ≥5%, ≥10%, ≥15%, and ≥20% body-weight loss from baseline. The 5% mark is widely cited in the obesity-medicine literature as the point at which weight-related health risks (blood pressure, glycemic control, lipids, sleep apnea, joint pain) start to measurably improve.
In the semaglutide arm, 86.4% of participants reached ≥5% loss by week 68. About 69% reached ≥10%, 50% reached ≥15%, and 32% reached ≥20%. In the placebo arm, those numbers were 31.5%, 12.0%, 4.9%, and 1.7%.
Even taking the placebo arm into account — which captures the effect of the lifestyle counseling alone — the gap between groups is large at every threshold. The "responder rate" framing is what tells you that the average is not being dragged up by a small number of unusually large responders.
“The proportion of participants who lost at least 5% of their body weight at week 68 was 86.4% with semaglutide and 31.5% with placebo… More participants in the semaglutide group than in the placebo group achieved weight reductions of 10% or more, 15% or more, and 20% or more.”
Plain-English read
Reading 86% as "almost everyone responds" is a fair shorthand — but it is not a guarantee that you will. Your own response depends on your physiology, your dose tolerance, how the medication is escalated, and how consistently the protocol is followed. The 5% threshold is meaningful because the health benefits start there — so the goal of any responsible program is to help you hit (and hold) at least that level, not to chase a specific number on the scale. Your clinician will calibrate to what is realistic and clinically valuable for you.
Peer-reviewed source
Once-Weekly Semaglutide in Adults with Overweight or Obesity
Wilding JPH, Batterham RL, Calanna S, et al. · New England Journal of Medicine, 2021 · DOI: 10.1056/NEJMoa2032183
Read the full study on NEJM