Ozempic or Mounjaro: Which Is Better for Weight Loss?

You typed 'Ozempic' but you probably want to know about Wegovy: here's why that matters

Picture this: you have read posts about people losing significant weight on Ozempic, and you want to know whether Mounjaro would do better. The frustration of hitting a wall of jargon when you just want a straight answer is completely understandable. So here it is.

Ozempic is semaglutide at doses up to 1mg, designed to manage blood sugar in type 2 diabetes. Wegovy is also semaglutide, but at a higher maintenance dose of 2.4mg (and now up to 7.2mg), with a separate MHRA licence specifically for weight management. The NHS medicines page for semaglutide explains the distinction clearly. Prescribing Ozempic for weight loss would be off-label; no reputable UK pharmacy should be doing that, and at nume (at our GPhC-registered pharmacy) our prescribers work strictly within licensed indications.

So when people ask whether Ozempic or Mounjaro is better, the meaningful clinical question is really Wegovy versus Mounjaro. That is the comparison we can make with evidence, and it is the one worth your time.

Wegovy vs Mounjaro: what the trial data says

Both medicines reduce appetite and slow gastric emptying, but they work differently. Mounjaro (tirzepatide) activates two gut-hormone receptors (GIP and GLP-1) while semaglutide targets GLP-1 alone. Whether that dual action translates to greater real-world weight loss was tested directly in the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025. Over 72 weeks in adults with obesity and no diabetes, tirzepatide produced meaningfully greater average weight reduction than semaglutide 2.4mg. A closer look at the SURMOUNT-5 findings sets out the numbers with their caveats.

Earlier, the STEP 1 trial showed semaglutide 2.4mg achieving around 15% average body-weight reduction over 68 weeks; SURMOUNT-1 showed tirzepatide reaching around 20–21% at its highest dose. Those are not directly comparable studies, but NICE's appraisal of tirzepatide (TA1026) acknowledged indirect comparisons that favour tirzepatide. The gap narrows with Wegovy's newer 7.2mg dose, where trials reported approximately 20.7% average weight loss over 72 weeks, which brings the two medicines much closer together.

The table below summarises the key factual differences.

These numbers come from controlled trials; individual results vary. You can compare the full clinical profiles of Mounjaro and semaglutide in more depth, including the side-effect profiles.

Side effects and practical differences worth knowing

Both medicines share a broadly similar side-effect profile: nausea, diarrhoea, constipation, indigestion and fatigue are the most commonly reported, usually most noticeable after starting or after a dose increase, and often settling within a couple of weeks. The NHS tirzepatide page and the NHS semaglutide page both list what to look out for and when to seek medical help.

One practical difference worth flagging is the contraception interaction. For tirzepatide specifically, women using oral contraceptives should use an additional non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because the pill's absorption may be reduced. NHS England's guidance on weight-management injections covers this in detail. No equivalent evidence currently exists for semaglutide. It is the kind of practical point that our clinical team goes through with you at consultation, it rarely makes headlines but it matters.

Mounjaro is the only dual-agonist weight-loss medicine licensed in the UK. Whether that mechanism suits you better than a GLP-1-only medicine is a clinical judgement, not something a comparison article can settle. For questions about switching between treatments, our guide on moving from Wegovy to Mounjaro is a practical starting point.

What IS licensed for weight loss, and how to access it through a regulated pharmacy

To be unambiguous: Ozempic is not a weight-loss medicine in the UK and cannot be legally prescribed as one. The two licensed injectable options for weight management are Mounjaro and Wegovy. Cost differences between them are real and worth understanding; our page on Wegovy and Mounjaro costs explains what the monthly figures typically include and exclude. For a broader look at how Mounjaro and Wegovy compare across outcomes, eligibility and practicalities, the full Mounjaro vs Wegovy comparison is the place to start.

At nume, a prescriber personally reviews every consultation (the same day) and works through both options with you based on your health history, not a preset algorithm. If you are eligible for either medicine, that conversation is the right place to make the decision. Speak to our prescribers by starting your free consultation. There is no fee for the consultation itself, and no obligation to proceed.