What wegovy studies for weight loss actually found

The STEP 1 trial: where the 15% figure comes from

STEP 1 is the foundation. Published in the New England Journal of Medicine in 2021, it recruited 1,961 adults with a BMI of 30 or above (or 27 with at least one weight-related condition) and no type 2 diabetes. Participants received either weekly semaglutide 2.4 mg or a placebo, alongside reduced-calorie guidance and regular activity encouragement. After 68 weeks, the semaglutide group had lost an average of around 14.9% of body weight versus roughly 2.4% in the placebo group. That gap is large by historical standards for a medicine without surgery.

A question our prescribers hear most weeks is whether those results reflect what happens in real clinical practice. The honest answer is that trial populations are carefully selected, so individual results will vary. The study excluded people with certain gastrointestinal conditions, a history of pancreatitis, and those who were pregnant or trying to conceive. That selection matters when you are interpreting the headline figure. The detail behind that study is worth reading if you want to understand exactly what the numbers mean for someone in your situation.

Beyond STEP 1: what the broader semaglutide trial programme showed

STEP 1 was not run in isolation. The STEP programme included several parallel trials examining semaglutide in people with type 2 diabetes (STEP 2), those who had already lost weight and were looking at maintenance (STEP 4), and specific groups including older adults. Across those trials, the weight-loss finding held: semaglutide consistently outperformed placebo by a substantial margin, and the side-effect profile was broadly consistent too, dominated by gastrointestinal symptoms (nausea, diarrhoea, constipation) that were most noticeable during dose increases and generally settled over time.

For readers thinking about how wegovy compares with tirzepatide (Mounjaro), the SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, reported greater average weight reduction with tirzepatide than with semaglutide 2.4 mg. That does not make wegovy an inferior medicine; it means the two work through different receptor pathways and produce somewhat different average results. Which suits an individual is a clinical question. You can read an overview of the longer-term semaglutide evidence for context on durability too.

The 7.2 mg approval: what the higher-dose evidence shows

Since the STEP programme concluded, Novo Nordisk ran trials on a higher semaglutide dose. The MHRA approved semaglutide 7.2 mg (initially available as three 2.4 mg pens weekly) in January 2026, and a dedicated single-dose 7.2 mg pen received MHRA approval on 14 April 2026. The trials reported average weight loss of around 20.7% over 72 weeks at the higher dose. That is meaningfully more than the 15% seen at 2.4 mg, and it places semaglutide closer to the tirzepatide results seen in SURMOUNT-1.

The 7.2 mg licence currently applies to adults with a BMI of 30 or above only. It does not extend to the BMI 27–29.9 range that the standard-dose licence covers when a weight-related condition is present. The starting dose remains 0.25 mg; the prescriber titrates upwards in the usual staged way. For anyone considering where wegovy sits in the broader picture of available treatments, the treatment overview page brings the evidence together alongside cost context. A transparent look at how private prices compare is also available on our price comparison page, which covers what different providers typically include in their headline figures.

What the studies do not resolve, and why the prescriber conversation matters

Clinical trials are designed to answer whether a medicine works on average, across a defined population, under controlled conditions. They are less good at predicting what happens for one specific person. Weight-loss outcomes in the STEP trials ranged widely: some participants lost significantly more than 15%, others less. Factors including baseline weight, medical history, how well the GI side effects are tolerated during dose increases, and how consistently the lifestyle changes are maintained all influence the result. The trial data is the strongest evidence available, but it is a population average, not a personal forecast.

That is precisely why the prescriber conversation is the right next step rather than a self-assessment against trial statistics. NICE's recommendation for semaglutide (TA875) sets out the clinical conditions under which it should be offered, and a summary of the individual studies can give you more to bring to that conversation. If you want to read more about semaglutide as a medicine before deciding, the semaglutide page covers the mechanism and licensed uses clearly. When you are ready to find out whether wegovy is clinically suitable for you, a free consultation with a GPhC-registered prescriber is the starting point, reviewed the same day, with no subscription required.