What the Wegovy weight loss studies tell you — and what to do with that information

What the STEP 1 trial actually measured

The decision about whether Wegovy is worth considering starts with understanding what the studies tested. STEP 1 was a 68-week, randomised, placebo-controlled trial involving over 1,900 adults. Participants had either a BMI of 30 or higher, or a BMI of at least 27 alongside a condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Everyone received counselling on diet and exercise alongside the injection. Nobody in STEP 1 had type 2 diabetes.

On that basis, the 2.4 mg dose produced an average weight loss of roughly 15% of starting body weight. Around one third of participants lost more than 20%. The placebo group lost about 2.4%. Those numbers are meaningful, but averages by definition hide a spread, some people lost considerably less, some more. The NHS patient information for semaglutide reflects these trial populations when it describes who the medicine is intended for.

A practical habit worth building before any consultation: pull up the NHS BMI calculator, enter your current height and weight, and note the figure. It takes under a minute and means you arrive at the conversation with a concrete starting point rather than an estimate.

How the 7.2 mg approval changed the picture

Since STEP 1, the evidence base has grown. On 14 April 2026, the MHRA approved a dedicated single-dose 7.2 mg Wegovy pen (the first of its kind) for adults with a BMI of 30 or above. Trial data at that dose reported approximately 20.7% average weight loss over 72 weeks, bringing results closer to those seen with tirzepatide at its highest dose. That approval followed an earlier January 2026 decision permitting 7.2 mg delivered as three 2.4 mg pens weekly; the new pen simplifies the weekly routine to a single injection.

If you have been reading comparisons between Wegovy and Mounjaro, this development matters. The head-to-head SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, found that tirzepatide produced greater average weight reduction than semaglutide 2.4 mg over 72 weeks. The 7.2 mg Wegovy data narrows that gap, though direct comparisons at the newer dose are still emerging. You can read more about how the studies compare on our overview of weight loss studies for Wegovy.

The titration schedule remains the same: treatment starts at 0.25 mg and increases approximately every four weeks, with 7.2 mg as the new ceiling. The prescriber sets the pace based on tolerability, not a fixed timetable.

Who the studies enrolled, and what that means for eligibility

Trial populations set the framework for licensing, which in turn shapes clinical eligibility. Wegovy is licensed in the UK for adults with a BMI of 30 or above, or 27 to 29.9 alongside at least one weight-related condition. Lower thresholds apply for some ethnic backgrounds under UK guidance, your prescriber can confirm whether that affects your assessment.

On the NHS, access under NICE's appraisal (TA875) is restricted to specialist weight management services, for a maximum of two years, and comes with strict comorbidity requirements and long waiting lists. Private prescribing through a regulated pharmacy follows the licensed criteria rather than the NICE pathway, which is why many people explore that route while NHS access catches up. If cost is part of your thinking, our guide to Wegovy pricing in the UK explains what a legitimate private price covers and what to watch out for.

One point the studies do not settle for you: whether Wegovy suits your specific health history. That is what a clinical consultation is for. The trials excluded people with a history of pancreatitis, medullary thyroid carcinoma, MEN2, and several other conditions, and those exclusions exist for good clinical reasons, not as red tape.

Side effects recorded in the studies, and what to watch for

The STEP trials reported a consistent side-effect profile across the semaglutide research programme. Gastrointestinal effects were the most common: nausea, vomiting, diarrhoea, constipation and indigestion. Most occurred after starting treatment or following a dose increase, and the majority settled within days to a couple of weeks. Stopping rates due to side effects were higher in the semaglutide group than placebo, so these are real considerations, not minor footnotes.

The MHRA has also flagged acute pancreatitis as an infrequent but potentially serious risk across GLP-1 medicines. Severe, persistent stomach pain that radiates to the back (with or without vomiting) warrants urgent medical attention. You can report any suspected side effect through the MHRA Yellow Card scheme. Our more detailed breakdown of how Wegovy works and what to expect covers these practical points further. Separately, a dedicated Wegovy study has examined a potential link between semaglutide and vision changes, which our page on the Wegovy and Ozempic vision loss study covers separately.

Wegovy is not recommended during pregnancy, whilst breastfeeding, or when trying to conceive. It is not licensed for anyone under 18. These are absolute boundaries, not guidelines to weigh up.

If the evidence looks relevant to your situation, the right next step is a clinical assessment, not a purchase. Start your free consultation and a GPhC-registered prescriber will review your answers the same day.