STEP-1 Explained: The 14.9% Semaglutide Weight-Loss Result
STEP-1 was the pivotal semaglutide weight-management trial. Over 68 weeks, participants on semaglutide 2.4mg lost about 14.9% of body weight on average versus about 2.4% on placebo — the result behind Wegovy's approval. The roughly 14.9% average applies to the approved 2.4mg product over 68 weeks alongside lifestyle support, and does not automatically transfer to compounded semaglutide, which carries no formulation-specific trial evidence.
- STEP-1 established semaglutide 2.4mg (Wegovy) for chronic weight management.
- Mean weight loss: ~14.9% over 68 weeks vs ~2.4% on placebo.
- Roughly a third of participants lost 20% or more of their body weight.
- Applies to FDA-approved semaglutide, not compounded formulations.
What STEP-1 measured
STEP-1 (Semaglutide Treatment Effect in People with Obesity) was the pivotal phase 3 trial that led to Wegovy's approval for chronic weight management. It enrolled nearly 2,000 adults with obesity, or overweight with a weight-related condition, and randomized them to weekly semaglutide 2.4 milligrams or placebo, both alongside lifestyle intervention.
The trial ran 68 weeks, long enough to capture the plateau where weight loss stabilizes. This duration matters: shorter trials can overstate ongoing loss by cutting off before the curve flattens.
The headline result
Participants on semaglutide lost about 14.9 percent of their body weight on average, compared with about 2.4 percent on placebo. For a 100-kilogram adult, that is roughly 15 kilograms of average loss attributable to the drug beyond lifestyle changes alone.
The distribution matters as much as the mean. Roughly a third of semaglutide participants lost 20 percent or more of their body weight, a degree of loss previously associated mainly with bariatric surgery. At the same time, a minority lost little, underscoring that response varies. The 14.9 percent figure is the population average, not a personal promise.
| Outcome | Semaglutide 2.4mg | Placebo |
|---|---|---|
| Mean weight loss | ~14.9% | ~2.4% |
| Lost ≥20% of weight | ~32% | ~2% |
| Duration | 68 weeks | 68 weeks |
| Applies to compounded? | No | — |
The limits of the number
Two caveats are essential. First, STEP-1 studied FDA-approved semaglutide at a specific dose and titration. Compounded semaglutide, oral semaglutide, and sublingual formulations were not studied here, and their results cannot be assumed to match. This is why applying the 14.9 percent figure to a compounded product is misleading.
Second, the weight loss depended on continued treatment plus lifestyle support. The STEP-1 extension data showed that stopping semaglutide led to substantial regain, which reframes the drug as a long-term therapy rather than a short course. The 14.9 percent is a with-treatment figure, not a permanent result.
| Trial | Focus |
|---|---|
| STEP-1 | Obesity, general population |
| STEP-2 | Type 2 diabetes |
| STEP-4 | Continued vs withdrawn treatment |
STEP-1 in context
STEP-1 sits within a larger programme. STEP-2 studied semaglutide in type 2 diabetes, STEP-3 added intensive behavioral therapy, and STEP-4 examined what happens on continued versus withdrawn treatment. Together they build a consistent picture: semaglutide produces substantial, durable weight loss while taken, with regain after stopping.
Compared with tirzepatide's SURMOUNT programme, semaglutide's average weight loss is strong but generally lower — the SURMOUNT-5 head-to-head confirmed this directly. STEP-1 remains the foundational semaglutide weight-loss evidence, and understanding exactly what it showed protects you from marketing that overstates or misattributes it.
Frequently asked questions
How much weight did people lose in STEP-1?
About 14.9% of body weight on average over 68 weeks on semaglutide 2.4mg, versus about 2.4% on placebo. Roughly a third lost 20% or more.
Does the 14.9% apply to compounded semaglutide?
No. STEP-1 studied FDA-approved semaglutide. Compounded formulations were not tested and their results cannot be assumed to match.
Do you regain weight after stopping?
STEP extension data showed substantial regain after stopping, which is why semaglutide is framed as a long-term therapy.
Sources
- Clinical trials via NEJM (STEP, SELECT, SURMOUNT, SURPASS).
- STEP-1 trial (Wilding et al., NEJM 2021).
- FDA — human drug compounding and GLP-1 status.