Wegovy percentage weight loss: what the trial evidence shows

You've read '15%' everywhere. Here's what that number actually means.

You're sitting with a number (15%) and trying to work out what it means for you personally. A reasonable instinct. The STEP 1 trial, published in the New England Journal of Medicine, randomised 1,961 adults with a BMI of 30 or above (or 27 with a weight-related condition) to either semaglutide 2.4mg weekly or placebo, both groups alongside reduced-calorie guidance and increased activity advice. The semaglutide group lost a mean of around 14.9% of their starting weight over 68 weeks. The placebo group lost around 2.4%.

The gap is striking. But 'mean' is doing a lot of work in that sentence. The trial included people who lost close to 30% and others who lost less than 5%. Individual responses to semaglutide weight loss vary considerably, and the research is honest about that. The percentage figure you'll land on depends on the dose you reach, how consistently you take it, what you eat alongside it, your activity level and how long you continue. That isn't a caveat to dismiss, it's the context that makes the number useful rather than misleading.

One misconception worth addressing gently: many people assume the 15% comes in the first few months. It doesn't. The titration schedule takes roughly 16 weeks to reach the full 2.4mg maintenance dose, and weight loss continues well beyond that point. If you're also tracking inflammation markers during treatment, our page on the hs-CRP reduction percentage seen with semaglutide shows how the medicine's effects extend beyond the scale. The final percentage at 68 weeks reflects sustained treatment, not a quick result.

The 7.2mg update changes the ceiling

Since STEP 1 was published, the picture has shifted. On 14 April 2026 the MHRA approved a dedicated single-dose 7.2mg Wegovy pen, the highest semaglutide dose yet licensed for weight management in the UK. Trials at this level reported an average weight reduction of around 20.7% over 72 weeks. That narrows the gap considerably with tirzepatide at its highest dose, and it means the percentage figures attached to Wegovy are no longer a fixed ceiling.

The 7.2mg pen is approved for adults with a BMI of 30 or above. The titration pathway still begins at 0.25mg, with gradual increases overseen by a prescriber; 7.2mg is the maximum, reached only after working through the lower steps. Whether a given patient reaches and maintains that dose is a clinical question. You can find the full UK approval detail in the MHRA's announcement on GOV.UK.

For context on what Wegovy costs in the UK private market, our Wegovy price comparison page sets out what a transparent treatment price should include and what to watch for when comparing providers.

Muscle loss and the percentage that matters beyond the scale

When a trial reports that participants lost 15% of their body weight, that percentage is total mass, fat and lean tissue combined. Some of that lean tissue is muscle. Research into semaglutide's effect on lean mass suggests the muscle-loss proportion is broadly in line with what happens in any calorie-restricted weight-loss programme, though GLP-1-induced appetite reduction can make it harder to eat enough protein to preserve muscle without conscious effort.

This matters practically. If a significant slice of the lost percentage is lean mass rather than fat, the metabolic benefit is smaller and the risk of regain once treatment stops is higher. Prescribers and dietitians consistently point to adequate protein intake (spread across meals) and resistance exercise as the levers for keeping lean mass up while the total weight comes down. None of that is complex, but it does require attention throughout treatment, not just at the start.

Our semaglutide overview covers the mechanism behind how the medicine works, and the Wegovy treatment page explains the full dose pathway and what clinical assessment involves. If you're weighing Wegovy against other options, the weight-loss treatments overview sets out what's currently licensed in the UK.

What the percentage tells you, and what it doesn't

A clinical trial average is a population statistic, not a personal prediction. What the STEP 1 percentage reliably tells you is that semaglutide produces clinically meaningful weight reduction well beyond what diet and activity achieve alone in a structured programme. What it can't tell you is exactly where you'll land.

A few things that genuinely influence individual outcomes: the dose reached (people who tolerate the full maintenance dose consistently lose more on average than those who stay at lower doses), duration of treatment (weight loss is still progressing at 68 weeks in many participants), baseline metabolic factors, and whether lifestyle changes run alongside the injection rather than in parallel without interaction. The STEP 1 initial weight-loss data gives a finer breakdown of how losses accumulate across the titration period, which is useful if you want to set realistic early expectations.

Wegovy is a prescription-only medicine. A prescriber reviews your health history, current medicines, BMI and any weight-related conditions before treatment is appropriate, the percentage figures from trials apply to people who met specific eligibility criteria, and that clinical check replicates those conditions for real-world use. If you'd like to understand whether treatment is suitable for your situation, our prescribers are available seven days a week: start your free consultation here.