Mounjaro or Wegovy for weight loss: which performs better?

What do the clinical trials show about weight loss on each medicine?

The clearest data comes from the phase 3 programmes for each medicine, and then from a direct comparison. In SURMOUNT-1 (72 weeks, involving thousands of adults with obesity and no diabetes), participants taking tirzepatide 15mg lost an average of around 20–21% of their body weight. Published in the New England Journal of Medicine, that figure has held up as one of the strongest results in weight-management medicine to date.

Wegovy's STEP 1 trial (68 weeks, semaglutide 2.4mg) produced average weight loss of around 15%. That is a substantial result by any historical benchmark. NICE's appraisal of semaglutide reflected that evidence base when recommending Wegovy through specialist weight management services.

Then came SURMOUNT-5, an open-label, head-to-head trial published in the New England Journal of Medicine in 2025, involving 751 adults with obesity and no diabetes, over 72 weeks. Tirzepatide produced a statistically greater average weight reduction than semaglutide 2.4mg. It is the most direct comparison available. NICE's committee discussion of tirzepatide also noted that indirect comparisons favour tirzepatide, which informed its recommendation in TA1026. A higher-dose Wegovy option (7.2mg) was approved by the MHRA in 2026 and narrows that gap in early data, but longer comparative evidence is still developing.

Numbers tell part of the story. Two people on the same medicine at the same dose can respond very differently, which is why a trial average is a starting point for a conversation, not a guarantee.

Do Mounjaro and Wegovy work differently, and does that matter for choosing?

Yes, and for some people the mechanism is clinically relevant. Wegovy acts on one receptor: GLP-1, a gut hormone that reduces appetite and slows stomach emptying. Mounjaro acts on two: GLP-1 and GIP. This dual-agonist profile is thought to explain the larger average weight loss seen in trials, though the precise reasons are still being studied.

Practically, the difference in mechanism can mean a difference in how each medicine feels. Some people find one easier to tolerate than the other, particularly around nausea and gastrointestinal effects. Both medicines share a GI-led side-effect profile (nausea, constipation, diarrhoea and bloating are common with each) but individual responses vary. There is no reliable way to predict in advance which will suit your system better; that is part of what the prescribing conversation is for.

Wegovy is also now available in tablet form. The MHRA approved oral semaglutide for weight management in June 2026, the first oral GLP-1 medicine licensed for weight loss in the UK. For people who prefer to avoid injections, that changes the comparison in a practical sense. Our treatment overview page covers the current options in more detail.

The comparison between semaglutide and Mounjaro goes beyond the average trial result, it includes tolerability, injection frequency, licensing nuance and your personal medical history.

What about Ozempic, is that better than Mounjaro or Wegovy for weight loss?

Ozempic is semaglutide, the same molecule as Wegovy, but it is licensed in the UK for type 2 diabetes, not for weight management. The MHRA has been clear on this distinction. A question our prescribers hear regularly is what's better: Ozempic or Mounjaro for weight loss, and the short answer is that Ozempic is not licensed for weight loss in the UK, so it falls outside the comparison entirely for that purpose.

Patients sometimes encounter Ozempic through private prescriptions for off-label use, or through unverified online sellers. Neither is a safe route to a weight-loss medicine. Comparing Ozempic and Mounjaro for weight loss is therefore not a like-for-like question: only two medicines are currently licensed in the UK for weight management in adults without diabetes, tirzepatide (Mounjaro) and semaglutide in its Wegovy formulation. Our Mounjaro vs Ozempic page explains the licensing distinction in full.

If you are managing type 2 diabetes alongside weight concerns, that changes the clinical conversation considerably, and your prescriber would factor in both conditions when considering any medicine.

Does one cost more than the other, and how do you compare them fairly?

Pricing depends on dose and provider. Since Eli Lilly raised Mounjaro's UK list price in September 2025, typical private market prices range from roughly £149 to £375 per month depending on the dose, figures that have been widely reported since the change. If you are weighing up the two options, our guide to what's best, Mounjaro or Wegovy, walks through the key factors to consider alongside cost. Our cost comparison page covers what drives the difference in more detail.

A fair comparison needs to include what the price actually covers: consultation, prescription, clinical aftercare and delivery are sometimes bundled, sometimes charged separately. The medicine cost alone is not the full picture. At nume, one price covers everything, no separate prescription fee, free next-working-day delivery, and 7-day aftercare included. Your order arrives in a plain box with DPD tracking sent to your phone, and the pen itself is exactly as the manufacturer produces it, sourced through the licensed UK supply chain.

For a prescription medicine, price is a reasonable consideration but the wrong primary filter. If you are still deciding between the two, our detailed look at what's better, Wegovy or Mounjaro, covers the clinical and practical considerations that go beyond the price tag. You can verify any online pharmacy on the GPhC register before placing an order; nume's registration number is 9012878.

Which suits you is a clinical decision our prescribers make with you. Start your free consultation and a GPhC-registered Independent Prescriber will review your answers the same day.