What the Wegovy Clinical Trial Evidence Actually Shows

How STEP 1 was designed and what its numbers mean in practice

STEP 1 recruited 1,961 adults with a BMI of 30 or above (or 27 and above with at least one weight-related condition) who did not have type 2 diabetes. Half received weekly semaglutide 2.4mg, titrated gradually over 16 weeks; the rest received a placebo. Everyone followed a reduced-calorie diet and increased their activity. After 68 weeks, the semaglutide group had lost a mean of around 14.9% of starting body weight, compared with 2.4% in the placebo group. Around a third of participants on the active treatment lost 20% or more.

Two things are worth holding onto when you read those numbers. First, they represent averages across nearly 2,000 people, individual results varied substantially. Second, weight loss slowed and then plateaued as the trial progressed, which is biologically expected: the body adapts. Most of the reduction had occurred by around week 60. The STEP 1 results in detail explain the titration schedule and what the plateau data looked like week by week.

If you are wondering whether results hold up when treatment stops, the STEP 4 withdrawal study offers the clearest answer, and it is sobering. Participants who switched to placebo at week 20 regained most of the weight they had lost by week 68. That finding shaped how prescribers think about Wegovy as a long-term, not short-term, intervention. More on that is covered on the STEP 4 trial page.

The wider STEP programme: different populations, consistent direction

STEP 1 is the most cited result, but the programme ran several parallel trials testing semaglutide in different populations. STEP 2 looked at adults with type 2 diabetes (a harder-to-treat group metabolically) and found roughly 9.6% mean weight loss at the 2.4mg dose. STEP 3 added intensive behavioural therapy and saw slightly larger losses, suggesting lifestyle support amplifies the medicine's effect. STEP 5 followed participants for two full years and found the reductions were broadly maintained, though with a gradual attenuation.

Across all the STEP trials, the side-effect profile was consistent: gastrointestinal symptoms (nausea, vomiting, diarrhoea, constipation) were the most common, reported most often in the first weeks and after dose increases, and generally settling with time. Serious adverse events were infrequent. The MHRA's Drug Safety Updates capture post-authorisation safety signals that build on the trial data, including the January 2026 update on acute pancreatitis as a rare but serious consideration.

NICE used the STEP evidence base when appraising semaglutide for weight management in the UK. Its recommendation (published as TA875) set out specific eligibility criteria, including a maximum treatment duration of two years within a specialist weight management service. Those criteria reflect what the trial data showed about sustained benefit and what the NHS can commission equitably. The semaglutide overview covers how that NICE recommendation translates to real-world access.

The 7.2mg dose: a newer chapter in the trial evidence

The original STEP programme tested semaglutide at 2.4mg weekly. A newer set of trials examined whether a higher dose could shift outcomes further. Results reported around 20.7% average weight loss over 72 weeks at 7.2mg, a meaningful step up. On 14 April 2026 the MHRA approved a dedicated single-dose 7.2mg pen for adults with a BMI of 30 or above, making it the highest licensed dose of semaglutide for weight management in the UK.

For context, this brings semaglutide's maximum efficacy closer to what tirzepatide achieved in the SURMOUNT programme, though head-to-head comparisons at the new dose are still limited. It also introduces a practical nuance: the 7.2mg approval applies to obesity (BMI 30 and above) and does not extend to the cardiovascular indication. Which dose is right for any individual depends on tolerance, response and clinical history, a prescriber works through that, not a webpage.

If you are trying to compare semaglutide and tirzepatide trial results side by side, the semaglutide trial overview sets them in context. And if permanence of weight loss is your specific question, the evidence on whether Wegovy results last draws on both the STEP 4 data and longer follow-up studies.

Who the trial results do and do not apply to

Trial populations are selected carefully, which means the results do not automatically translate to every person asking about Wegovy. STEP 1 excluded people with type 2 diabetes, those who had previously taken a GLP-1 medicine, and those with active major psychiatric illness or recent cardiovascular events. Most participants were White European. That matters because response to treatment can differ by ethnicity, age, starting BMI, and metabolic profile, even if the direction of effect is broadly similar.

UK licensing reflects the trial populations: Wegovy is licensed for adults with a BMI of 30 or above, or 27 and above with at least one weight-related condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under NICE guidance. Pregnancy, breastfeeding, trying to conceive, and being under 18 are all situations where semaglutide is not recommended, a prescriber goes through each of these at consultation.

It is also worth noting that the trials ran alongside diet and lifestyle support. Semaglutide was not tested as a standalone intervention in isolation from any behaviour change. Prescribers at services like ours are clear about that expectation from the start. For a straightforward read of what Wegovy is and how it is used in the UK, the pillar page pulls together licensing, eligibility and access in one place. If you think you might be suitable and want to talk it through, you can start a free consultation, a named GPhC-registered prescriber reads every response the same day, not software. Some people find it useful to do this on a Monday if they want any prescription dispatched before the week gets busy, though orders placed before 12pm on any working day qualify for same-day dispatch once approved. That is not a nudge, just practical information.