Wegovy's impact on weight and health: what the evidence shows

What STEP 1 actually measured — and what those numbers mean in practice

The STEP 1 trial is the foundation for most of what clinicians say about Wegovy's impact. It randomised 1,961 adults with obesity or overweight plus at least one weight-related condition to either semaglutide 2.4 mg weekly or placebo, alongside lifestyle changes, for 68 weeks. The semaglutide group lost an average of around 15% of body weight; the placebo group lost roughly 2.4%. That gap matters because it reflects the medicine's biological effect on top of the lifestyle support both groups received.

Beyond weight, the trial recorded reductions in waist circumference, systolic blood pressure and fasting blood glucose. These are the kinds of outcomes clinicians watch because they track cardiovascular risk, not just a number on the scale. The NHS medicines page for semaglutide summarises the licensed uses and expected effects in plain language, and it is worth reading if you want to understand what the medicine is and is not designed to do.

One thing the trial also confirmed: the effect builds gradually. Most of the weight reduction accumulates over the first 40 to 60 weeks as the dose titrates upward. People who expect a dramatic change in the first month tend to feel let down; people who understand the gradual mechanism tend to stay with treatment long enough to reach the results the data describe.

The higher-dose picture: what the 7.2 mg approval adds

In January 2026 the MHRA approved a 7.2 mg maintenance dose of semaglutide for weight management, initially administered as three 2.4 mg pens per week. On 14 April 2026, the MHRA approved a dedicated single-dose 7.2 mg pen, making the higher dose considerably more practical. Trials at this dose reported average weight loss of around 20.7% over 72 weeks — closing much of the gap with tirzepatide's trial results and offering a meaningful step up for people on the standard maintenance dose who have reached a plateau.

The 7.2 mg pen is licensed for adults with a BMI of 30 or above. The starting dose remains 0.25 mg, titrated upward by a prescriber roughly every four weeks; the 7.2 mg level is the ceiling, not the starting point. Whether a specific pen format or dose is right for any individual patient is always a clinical decision, and availability of particular presentations is confirmed at the point of consultation rather than assumed in advance.

If you are weighing up Wegovy against other options, our treatment overview covers the licensed medicines currently available through a regulated UK pharmacy.

Effects that sit alongside weight loss, and effects to prepare for

The honest picture of Wegovy's impact includes both its benefits and its side-effect profile. Gastrointestinal effects are the most commonly reported: nausea, constipation, diarrhoea, indigestion and occasionally vomiting, particularly in the weeks after a dose increase. For most people these are mild to moderate and settle as the body adjusts. They are worth knowing about in advance rather than discovering mid-way through.

There are also interactions to be aware of. Women taking oral contraceptives alongside tirzepatide or semaglutide injections should discuss their contraception with a prescriber; the specific interaction details depend on which medicine is involved, and our page on Wegovy's impact on birth control covers this properly. Sleep is another area patients sometimes ask about, and there is a separate page on whether Wegovy affects sleep for anyone who has noticed changes.

We know it can feel overwhelming to read through a long list of possible effects when you are already uncertain whether this is the right route for you. That is a very normal place to be at this point. The aim here is to give you an accurate picture so that any conversation with a prescriber is grounded in facts, not guesswork.

On the supply side, it is worth knowing that semaglutide purity and supply-chain integrity matter considerably when choosing a provider; the counterfeit-pen problem in the UK has made this a genuine clinical concern, not just a consumer one.

Who the evidence applies to, and how to take the next step

The STEP 1 population had a mean BMI of around 38, and most participants had at least one weight-related condition such as high blood pressure or raised cholesterol. The trial results apply most directly to that population. Wegovy's UK licence covers adults with a BMI of 30 or above, or 27 to 29.9 with at least one weight-related condition, as confirmed by NICE's technology appraisal TA875. BMI alone does not determine suitability; a prescriber looks at the whole picture, including medical history, current medicines and individual circumstances.

The evidence base for Wegovy is substantial. It is also not a guarantee of any specific personal result, the trial averages include people who lost considerably more and people who lost less. A prescriber reviews that detail with each patient at the point of consultation. For more background on semaglutide as the active ingredient, our semaglutide overview is a good starting point, and our Wegovy treatment page covers how the medicine is used in practice at nume.

If you decide to explore treatment, start your free consultation and a GPhC-registered prescriber will review your details the same day, through a service designed for people who want to access Wegovy without needing to contact their GP.