What's Wegovy and how does it work for weight loss?

What's actually in Wegovy, and what does it do in the body?

Wegovy's active ingredient is semaglutide. It belongs to a class called GLP-1 receptor agonists, meaning it binds to the same receptors that the body's own gut hormone GLP-1 activates after a meal. When those receptors fire, they do several things at once: they signal the hypothalamus to reduce appetite, slow the rate at which food leaves the stomach, and help regulate blood-glucose levels. The net effect, over weeks, is that most people feel full sooner and find high-calorie foods less appealing than before.

Semaglutide itself is not new. The same molecule has been used in type 2 diabetes treatment for years. Wegovy is the formulation developed specifically for weight management, at a higher dose than its diabetes counterpart. A common question our prescribers hear is whether Ozempic and Wegovy are interchangeable; they share the same active ingredient, but Ozempic is licensed for type 2 diabetes, not weight loss, and the two should not be treated as equivalent options. For a deeper look at how semaglutide behaves as a drug class, the semaglutide overview covers the pharmacology in plain terms.

Wegovy is delivered via a pre-filled pen, injected once a week under the skin of the abdomen, thigh or upper arm. The injection itself is brief; most people manage it without difficulty after the first dose.

What's Wegovy for, and who can be prescribed it in the UK?

The UK licence covers adults with a BMI of 30 or above, or a BMI of 27 to 29.9 alongside at least one weight-related condition such as high blood pressure, raised cholesterol, prediabetes or obstructive sleep apnoea. It is prescribed alongside a reduced-calorie diet and increased physical activity, not as a standalone solution. A 2.5 kg/m² lower threshold applies for some ethnic backgrounds under UK guidance.

NICE has also appraised Wegovy under its technology appraisal TA875, recommending it through specialist weight management services for up to two years, subject to clinical criteria. NHS access remains limited and waiting lists are long at many centres, which is why private routes through a registered pharmacy exist. For a fuller breakdown of the conditions Wegovy is indicated for, see the dedicated uses page.

BMI alone does not determine approval. A prescriber weighs up your full medical picture: medications, existing conditions, family history and your goals. That assessment is what the clinical review exists to do.

How much weight do people lose on Wegovy in practice?

The headline figure comes from the STEP 1 trial: adults with obesity and no diabetes lost an average of around 15% of body weight over 68 weeks at the 2.4 mg maintenance dose, compared with roughly 2.4% in the placebo group. Those are averages across thousands of participants; individual results vary, and weight loss is not guaranteed. You can read the published trial data on the Wegovy results and statistics page.

In January 2026 the MHRA also approved a higher 7.2 mg dose of Wegovy, and a dedicated single-dose 7.2 mg pen followed in April 2026. Trials at this dose reported average weight loss of around 20.7% over 72 weeks, bringing it closer to the results seen with tirzepatide. If you are weighing up which medicine might suit you, the Wegovy vs Mounjaro comparison sets out the evidence side by side.

Results depend on dose, adherence, diet and activity. Wegovy is not assessed or licensed for quick or cosmetic weight loss; the MHRA is clear on that point. Treatment is a medium-to-long commitment, not a short course.

What are the most common side effects people notice on Wegovy?

The side-effect profile is led by the gut. Nausea is the most frequently reported, followed by vomiting, diarrhoea, constipation and indigestion. These tend to be most noticeable in the first few weeks or after a dose increase, and they settle for most people as the body adjusts. Starting on the lowest dose and titrating gradually is specifically designed to reduce this burden.

Less common but more serious effects to be aware of include acute pancreatitis. The MHRA highlighted this risk in a Drug Safety Update in January 2026: if you develop severe stomach pain that spreads to your back, with or without vomiting, seek urgent medical attention. Gallbladder problems and, rarely, serious allergic reactions have also been reported. The NHS semaglutide medicines page lists the full side-effect profile in patient-friendly language.

Wegovy is not recommended during pregnancy, while breastfeeding, or for anyone trying to conceive. It is not licensed for under-18s. If you take oral contraceptives, your prescriber will want to review your contraception plan, as there is guidance on timing and method for women on GLP-1 medicines. Anyone due surgery should tell their anaesthetist they are on a GLP-1 treatment. If you are also taking naltrexone, it is worth reading about using naltrexone and Wegovy together before discussing the combination with your prescriber. For questions about timing your weekly dose, the guide on when to inject Wegovy covers the practicalities, including what to do if a dose falls on a bank holiday or just after payday when a repeat hasn't arrived yet.

If you would like a prescriber to review your medical history and assess whether Wegovy is appropriate for you, start your free consultation with the nume clinical team today.