What the semaglutide trials found — and what the results actually mean

The biggest misconception: 'it's just a trial drug, we don't know if it works long-term'

Semaglutide for weight management has one of the more substantial evidence bases of any medicine in this space. The STEP programme (Semaglutide Treatment Effect in People with Obesity) ran across multiple countries, with thousands of participants and follow-up periods of up to 68 weeks in STEP 1 and longer in subsequent studies. This is not a handful of early-phase data, it is the evidence base that led NICE to recommend semaglutide for use in England.

The long-term picture is more nuanced, though. STEP 4 enrolled adults who had already taken semaglutide for 20 weeks and then randomised them either to continue or to switch to placebo. Those who continued lost a further 7.9% of their body weight; those who stopped regained most of what they had lost within 48 weeks. That result is not a flaw in the trial, it reflects how the medicine works. Weight tends to return when treatment stops, which is why semaglutide is considered an ongoing rather than short-course therapy for most people. You can read more about what the STEP 4 withdrawal findings mean in practice.

NICE's appraisal (technology appraisal TA875) recommended semaglutide for NHS use in specialist weight management settings, which reflects the quality of the trial evidence, not a tentative endorsement.

What STEP 1 actually measured, and who was in it

STEP 1 is the study most people refer to when discussing semaglutide trial results. Published in the New England Journal of Medicine, it recruited 1,961 adults with a BMI of 30 or above (or 27 with at least one weight-related condition), all without type 2 diabetes. Participants were randomised to semaglutide 2.4mg once weekly or placebo, both alongside reduced-calorie diet guidance and increased physical activity support.

After 68 weeks, average weight reduction in the semaglutide group was around 14.9% of starting body weight, compared with 2.4% in the placebo group. Around one in three participants lost more than 20% of their body weight on the active treatment. Blood pressure, waist circumference and certain cardiometabolic markers also improved. A fuller breakdown of the STEP 1 findings covers the secondary outcomes in more detail.

One practical note: STEP 1 included structured lifestyle support alongside the medicine. The trial results reflect that combination, not the injection alone, something worth bearing in mind when interpreting the headline figures. For a broader look at how the semaglutide weight-loss trial programme was designed, that page covers the methodology across the STEP studies.

The 7.2mg dose: what more recent trial data showed

The standard maintenance dose in the original STEP programme was 2.4mg weekly. More recent research examined whether a higher dose could improve outcomes further. The data pointed to meaningful additional weight loss: trials at 7.2mg reported an average reduction of around 20.7% of body weight over 72 weeks, which narrows the gap with tirzepatide's trial results considerably.

On 14 April 2026, the MHRA approved a dedicated single-dose 7.2mg pen (one pre-set weekly injection) for adults with a BMI of 30 or above. The starting dose remains 0.25mg, titrated by a prescriber, typically in monthly steps, up to the 7.2mg maximum. That approval is specific to adults with obesity and does not extend to the lower BMI threshold or to cardiovascular indications. If you want to understand the OASIS trial evidence that supported the oral semaglutide approval, that sits in a separate evidence stream.

The question of which dose is right for an individual, and when to titrate, is exactly the kind of clinical judgement that belongs with a prescriber rather than a webpage. That said, understanding the Wegovy dosing pathway is useful context before a consultation.

What the trials mean for someone considering treatment now

Trial populations are not the same as every individual who might be prescribed a medicine. STEP 1 excluded people with type 2 diabetes, active eating disorders, certain cardiovascular conditions, and those who were pregnant or planning to conceive. Real-world results vary, adherence, starting weight, diet, activity levels and individual biology all play a role. The trials give a population-level signal; your own response is something a prescriber monitors over time.

The most common side effects in the STEP trials were gastrointestinal: nausea, vomiting, diarrhoea and constipation, concentrated at the start of treatment and after each dose increase, and generally easing within a couple of weeks. Around 4.5% of participants discontinued the active treatment due to gastrointestinal effects. The NHS semaglutide information page covers side effects and interactions in plain English.

If the trial evidence has convinced you to explore this properly, a free consultation with our prescribers is a sensible starting point. Our clinical team, which you can read about at our clinical team page, reviews every application the same day. Worth checking whether you meet the eligibility criteria before booking anything, the consultation itself will do that, at no cost. Before that, a look at how Wegovy is priced for private prescriptions may help set expectations.