What the semaglutide phase 3 trials actually found — and what it means for you

The STEP trials: what was actually studied, and why the design matters

Understanding the STEP programme is easier if you start from the question each trial was designed to answer. STEP 1 asked what semaglutide does in adults with obesity and no diabetes, 1,961 participants, 68 weeks, 2.4mg weekly versus placebo alongside a reduced-calorie diet and increased activity. The average weight loss of around 15% in the semaglutide group was not a best-case result; it was the mean across the whole treated population, including people who experienced significant side effects or did not reach the full maintenance dose.

STEP 2 looked at adults with type 2 diabetes alongside obesity, a population where weight loss tends to be smaller, and it was. STEP 3 added intensive behavioural therapy to the mix. STEP 4 examined what happens when you stop: participants who switched to placebo after 20 weeks regained most of the weight lost, which is consistent with how GLP-1 medicines work, appetite returns when the medicine does. Together, the trials answer a cluster of practical questions: how much weight can I expect to lose, does it matter if I have diabetes, and what happens if I stop?

If you want to read the NHS medicines guidance on semaglutide before exploring your own options, that is a good place to start, it translates the clinical evidence into plain terms.

From trial data to UK licence: what NICE and the MHRA concluded

Phase 3 evidence does not automatically become clinical practice. The MHRA assessed the trial programme and licensed Wegovy for weight management in the UK, and the NICE technology appraisal (TA875) then set the conditions under which it can be recommended on the NHS. NICE concluded that semaglutide should be used for a maximum of two years, within a specialist weight management service that provides multidisciplinary support. On the NHS, that means a waiting list and specific eligibility criteria, a BMI of 35 or above with at least one weight-related condition, with thresholds 2.5 kg/m² lower for South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds.

The gap between the trial setting and NHS clinical practice is worth thinking about. In STEP 1, participants received regular support alongside the medicine. NICE's specialist-service requirement is designed to replicate some of that structure. If you are considering the private route, the clinical scaffolding matters just as much, which is one reason our prescribers review every consultation personally rather than leaving it to automated systems.

Wegovy is also licensed in the UK for reducing the risk of major cardiovascular events in eligible adults, and a conditional approval for a form of fatty liver disease was granted in July 2026. Both reflect how the evidence base for semaglutide continues to grow beyond the original STEP weight-loss data.

The dose titration schedule and what the phase 3 trials used

The licensed maintenance dose tested in STEP 1 was 2.4mg weekly. Reaching it takes time, the titration pathway moves through 0.25mg, 0.5mg, 1.0mg and 1.7mg, spending roughly four weeks at each level, before arriving at 2.4mg. That structure exists because the gastrointestinal side effects common to GLP-1 medicines (nausea, loose stools, constipation, indigestion) are usually most noticeable during dose increases and tend to settle as the body adjusts.

In April 2026, the MHRA also approved a dedicated 7.2mg single-dose pen as the new maximum for adults with a BMI of 30 or above, following trial data showing average weight loss of around 20.7% at that dose over 72 weeks. That approval narrowed the gap with the tirzepatide data, if the comparison between the two interests you, our Wegovy treatment overview covers it in more detail. Specific dose availability is confirmed at the point of clinical assessment rather than before it, since the prescriber needs to know where you are in your treatment journey.

If you are already on treatment and wondering about a particular dose step, our guide to the 0.5mg dose and the 0.25mg starter information may be useful background, though any actual titration decision sits with your prescriber and the patient information leaflet, not a content page. If you are specifically moving up to the third dose level, our guide to the 1.0mg semaglutide step walks through what to expect at that stage of titration.

Making sense of the numbers before you decide

If you have spent time reading about semaglutide, you may be feeling slightly overwhelmed by now, that is entirely understandable. The trial data, the NICE criteria, the dose schedule and the newer 7.2mg approval all layer on top of each other quickly.

The practical question most people arrive at is simpler: does this treatment suit my situation, and can I get it safely? The phase 3 evidence tells you what semaglutide does in a large, well-monitored trial population. It cannot tell you what will happen for you specifically, your medical history, current medicines and clinical picture all shape that, which is exactly why a prescriber's assessment matters before a single pen is dispensed.

On the cost side of the decision, if you want to understand what you should reasonably expect to pay, our guide to finding best value Wegovy in the UK explains what a legitimate private prescription typically includes and what the range across providers looks like, worth reading before treating any headline figure as the full picture. And if you want to explore the broader weight-loss treatment options before committing to semaglutide specifically, that overview covers the alternatives side by side.

When you are ready to talk to someone clinical, our prescribers review every consultation the same day, a real clinician reads your answers, not a queue for an automated system. You can start your free consultation whenever the time feels right.