STEP 1 was the foundational randomized controlled trial that established once-weekly semaglutide 2.4 mg as an effective tool for chronic weight management. It enrolled 1,961 adults with overweight or obesity (without type 2 diabetes) at 129 sites in 16 countries, and ran for 68 weeks.
Half the participants received semaglutide; half received a placebo. Both groups received the same lifestyle intervention — counseling on diet and physical activity. The study was double-blinded, meaning neither participants nor researchers knew who was receiving the medication, which is the gold standard for separating real treatment effect from expectation.
At week 68, the semaglutide group had lost an average of 14.9% of their starting body weight. The placebo group had lost 2.4%. That gap — the part attributable to the medication itself, on top of lifestyle change — is the headline number cited across the homepage.
The most common side effects were gastrointestinal — nausea, diarrhea, vomiting, and constipation — typically mild to moderate and concentrated during dose escalation. Serious adverse events were uncommon and similar between groups.
“The mean change in body weight from baseline to week 68 was −14.9% in the semaglutide group as compared with −2.4% in the placebo group, for an estimated treatment difference of −12.4 percentage points.”
Plain-English read
A few things to remember when you read a number like 14.9%. It is an average across nearly two thousand people — some lost more, some lost less. It comes from a structured trial with clinician check-ins, dose adjustments, and the same lifestyle support we offer here. And it is meant to give you a realistic baseline for what is possible — not a promise. Your own results depend on your starting point, your protocol, and your follow-through, and your clinician will help you set goals that make sense 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