Mounjaro or Ozempic for weight loss: which one should you actually consider?

Why the Mounjaro vs Ozempic framing gets the question slightly wrong

Ozempic is semaglutide dosed at up to 1 mg weekly, approved in the UK by the MHRA for blood-sugar control in type 2 diabetes. The NHS medicines page for tirzepatide and equivalent regulatory documents are clear: prescribing Ozempic for weight loss alone would be an off-label use, and responsible UK prescribers and pharmacies do not do this. If a seller is offering Ozempic specifically for weight loss without a diabetes diagnosis, that is a clinical red flag.

The weight-loss-licensed version of semaglutide is Wegovy, dosed at up to 2.4 mg weekly (and now up to 7.2 mg with the newly approved higher-dose pen). So when people ask whether Ozempic or Mounjaro is better for losing weight, the question they usually mean is: how does tirzepatide compare with semaglutide at its full weight-management dose? That is the comparison that has real clinical evidence behind it, and it is explored in the sections below. You can read a fuller breakdown on our Mounjaro vs Ozempic overview page.

The short version: if weight loss is the goal, the relevant choice is between Mounjaro and Wegovy, both of which are UK-licensed for that purpose and both of which our pharmacy team can prescribe following a clinical assessment.

What the head-to-head trial data shows, and what it doesn't settle

Until 2025, direct comparisons between tirzepatide and semaglutide 2.4 mg relied on indirect analyses across separate studies. The SURMOUNT-5 trial changed that. Published in the New England Journal of Medicine in 2025, it randomised 751 adults with obesity and no diabetes to either tirzepatide or semaglutide 2.4 mg weekly for 72 weeks. On average, participants taking tirzepatide lost more body weight than those on semaglutide, a finding that fed into NICE's appraisal of tirzepatide (TA1026), which noted indirect comparisons also favour tirzepatide.

That said, averages rarely predict individual outcomes. Semaglutide 2.4 mg produces clinically significant weight loss in its own right, around 15% on average over 68 weeks in the STEP 1 trial. The 7.2 mg dose now approved by the MHRA narrows the gap further, with trials reporting approximately 20.7% average loss at 72 weeks. For some people, semaglutide is better tolerated; for others, tirzepatide fits their situation more naturally. The table below sets out the key figures side by side.

Sources: SURMOUNT-1, New England Journal of Medicine; NICE TA1026; MHRA approval announcements.

Side effects, tolerability and the practical difference between two injections

Both medicines share a gastrointestinal side-effect profile: nausea, loose stools, constipation, reflux and fatigue are the most commonly reported, typically peaking around a dose increase and settling within one to two weeks for most people. Neither is comfortable to start on, the titration schedule exists precisely to give your body time to adjust, which is why you begin at a much lower dose than the eventual maintenance level.

One practical difference worth knowing about: for women using oral contraceptive pills, tirzepatide slows gastric emptying enough that pill absorption may be affected for the first four weeks of treatment and for four weeks after each dose increase. Adding a barrier method during those windows is the standard recommendation. The same caution applies to transdermal HRT: NHS guidance suggests discussing patch or gel alternatives while on tirzepatide. The NHS England page on weight-management injections covers both points clearly. There is no equivalent evidence of reduced pill effectiveness with semaglutide, though any medicine change warrants a conversation with your prescriber.

If you are considering switching between these medicines, the clinical picture needs re-examining from scratch. Our page on switching from Mounjaro to semaglutide for weight loss covers what that process involves.

Which one is right for you, and how to find out

There is no universal answer here, which is why the heading doesn't pretend there is. Mounjaro has produced greater average weight loss in head-to-head trials, and its dual mechanism is the only one of its kind licensed for weight management in the UK. Wegovy at either dose is a well-evidenced alternative, and the newer 7.2 mg option has meaningfully closed the gap. Ozempic, as a UK medicine, is not part of this decision for someone without type 2 diabetes.

The factors that actually determine which treatment a prescriber would recommend include your BMI, any existing conditions, current medicines, contraceptive method, and how you've responded to treatment before. If you've already tried one and want to reassess, that history matters too. A more detailed side-by-side breakdown of the two licensed options is on our Wegovy vs Mounjaro comparison page, including cost context. You can also explore which works better for weight loss in more depth if evidence detail is what you're after.

If you're ready to have that clinical conversation, check your eligibility with our prescribers. The consultation is free, reviewed personally the same day, and there's no obligation to proceed. Some people find it helpful to do this around a natural break (the start of a new month, or after a holiday) simply because treatment works best when you can commit to the routine from day one.