What the Wegovy clinical trials actually found — and what it means for you

You've read the 15% figure, here's the trial behind it

The number quoted most often comes from STEP 1, a 68-week randomised controlled trial of 1,961 adults. Participants had a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure or raised cholesterol, and none had type 2 diabetes. Everyone received structured lifestyle counselling; half also received weekly semaglutide injections titrated up to 2.4mg, and half received a placebo. The semaglutide group lost an average of around 15% of their starting body weight. The placebo group, also getting lifestyle support, lost closer to 2.4%. That gap (published in the STEP 1 paper in the New England Journal of Medicine) is the reason Wegovy drew serious attention from regulators and clinicians rather than being filed alongside earlier weight-loss medicines with more modest effects. A question our prescribers hear most weeks is whether people who didn't stick rigidly to the diet plan still saw results: the trial design used intention-to-treat analysis, so yes, the 15% figure includes participants who weren't perfectly adherent. That makes it a realistic average rather than a best-case scenario. You can read more about how the wider Wegovy trial results break down across different participant groups.

The STEP programme didn't stop at one trial

STEP 1 was the starting point, not the whole story. The STEP programme ran several parallel trials testing semaglutide 2.4mg in different populations. STEP 2 focused on adults with type 2 diabetes alongside obesity, finding somewhat lower but still clinically meaningful weight loss, unsurprising, since the biology of weight regulation in diabetes differs. STEP 4 tested what happened when participants who had already lost weight on semaglutide were switched to placebo: they regained much of the weight, which confirmed the medicine works while you take it rather than resetting your body's set-point permanently. STEP 5 followed participants for two years and showed the weight loss was largely maintained at 104 weeks, which matters for both clinical planning and NHS approval decisions. NICE's appraisal of semaglutide (TA875) considered this accumulated evidence base before recommending it for NHS use within specialist weight management services. The programme as a whole involved tens of thousands of participants across multiple countries, which gives the safety profile substantial statistical weight. Details on the wider semaglutide clinical trial programme cover these studies in depth.

The 7.2mg trials and where the evidence now stands

After the original 2.4mg approvals, Novo Nordisk ran further trials testing a higher 7.2mg dose, building on the clinical foundations established across the STEP programme. The MHRA approved 7.2mg semaglutide for weight management in January 2026, initially supplied as three 2.4mg pens weekly, and then approved a dedicated single-dose 7.2mg pen on 14 April 2026. Trial data for the higher dose reported approximately 20.7% average weight loss over 72 weeks, narrowing the gap with tirzepatide (Mounjaro) results seen in the SURMOUNT-5 head-to-head study. That higher-dose pen is licensed for adults with a BMI of 30 or above; it is not indicated at lower BMIs or for the cardiovascular risk-reduction licence. The 7.2mg semaglutide trial data page goes further on the methodology. For context on what private treatment typically costs now that the evidence base has expanded, the Wegovy prices page covers current market context without the marketing gloss. The MHRA announcement on the 7.2mg single-dose pen sets out the approval details precisely.

From trial population to clinical suitability, not the same thing

Trial populations are carefully selected; real patients are not. The STEP trials excluded people with a history of pancreatitis, certain thyroid conditions, and several other factors. That's one reason why a prescriber's assessment matters even when the trial evidence looks straightforwardly positive. Semaglutide is a GLP-1 receptor agonist: it slows gastric emptying, reduces appetite signals and influences how the brain processes food cues. The most common side effects across the STEP trials were gastrointestinal (nausea, loose stools, vomiting, constipation, reflux) and these were generally mild to moderate, peaking in the early weeks of treatment and at each dose step. Serious adverse events were uncommon, though pancreatitis, gallbladder problems and allergic reactions are listed in the prescribing information and require prompt medical attention if they occur. Women using oral contraceptives should discuss their contraception with a prescriber before starting, since GLP-1 medicines can affect oral absorption. None of this makes the trial data less compelling; it means the data sits alongside a clinical conversation, not instead of one. If you're weighing up whether to pursue treatment, our Wegovy overview covers eligibility in full, and you can speak to our prescribers through a free consultation that's reviewed the same day by a GPhC-registered Independent Prescriber.