Mounjaro versus Ozempic: the comparison that matters most

You've searched 'Mounjaro versus Ozempic', here's the situation you're actually in

Most people typing this comparison have heard both names, suspect they do similar things and want to know which is better for losing weight. It's a question our prescribers hear most weeks, and it deserves a straight answer rather than a hedge.

Ozempic contains semaglutide at doses up to 1mg and is licensed by the MHRA to treat type 2 diabetes. It works well for that purpose. What it does not have is a UK authorisation for weight management. Using it purely for weight loss would mean a prescriber issuing it outside its licence, something no regulated UK pharmacy should be doing. If you've seen it offered online without a diabetes diagnosis, that's worth treating as a red flag.

Mounjaro contains tirzepatide. It is licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 and above alongside a weight-related condition such as high blood pressure or high cholesterol. It is also licensed for type 2 diabetes. So the choice for someone seeking weight-loss treatment is not really Mounjaro versus Ozempic, it's Mounjaro versus Wegovy, because Wegovy (semaglutide 2.4mg) is the weight-management-licensed form of semaglutide. That distinction is not a technicality; it determines which treatment a prescriber can lawfully offer you.

The rest of this page covers how the two medicines compare where it genuinely matters: mechanism, trial evidence, side-effect profile and access.

How the mechanisms differ, and why tirzepatide's dual action changes the numbers

Both medicines slow gastric emptying and reduce appetite by mimicking gut hormones your body releases after eating. The difference is in the receptors they activate.

Ozempic and Wegovy both activate the GLP-1 receptor. Mounjaro activates two: GLP-1 and GIP. GIP (glucose-dependent insulinotropic polypeptide) plays a separate role in fat metabolism and energy balance. Activating both pathways together appears to produce greater appetite suppression and, in trials, greater weight reduction than GLP-1 alone at comparable doses.

The trial evidence reflects this. In SURMOUNT-1 (a 72-week study involving thousands of adults with obesity) participants on tirzepatide at the highest dose lost an average of around 20–21% of body weight, as published in the New England Journal of Medicine. STEP 1, the equivalent 68-week semaglutide 2.4mg trial, reported an average loss of around 15%. The SURMOUNT-5 head-to-head study then compared both medicines directly and found tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks, results NICE cited in its appraisal of tirzepatide (NICE TA1026).

None of those figures apply to Ozempic at its 1mg diabetes dose. The semaglutide weight-loss trials all used the 2.4mg weekly dose available only as Wegovy. If you want to understand how semaglutide versus Mounjaro compares across the full picture of licensed doses and trial data, our dedicated page covers that in detail.

Side effects: broadly similar, with some differences worth knowing

The side-effect profile of both medicines is dominated by gastrointestinal symptoms. Nausea, loose stools, constipation, indigestion and reduced appetite are common with both, most pronounced after starting or after a dose increase, and they often settle within the first few weeks. That pattern appears across NHS guidance on tirzepatide and the equivalent semaglutide information.

Pancreatitis is a known but infrequent serious risk with GLP-1 class medicines generally, including tirzepatide. Severe, persistent abdominal pain that radiates to the back needs urgent medical attention. The MHRA highlighted this risk in a Drug Safety Update in January 2026 and it applies across the class.

One practical difference for women taking oral contraceptives: for tirzepatide specifically, NHS guidance advises adding a non-oral method of contraception during the first four weeks of treatment and for four weeks after each dose increase, because slowed digestion may reduce pill absorption. There is no equivalent specific guidance for semaglutide. If you're currently on Ozempic for diabetes and your doctor is considering a switch to Mounjaro or Wegovy, that is worth raising at your appointment. The nume FAQs cover this and other common questions in more detail.

Missed doses, dose timing and any changes to your schedule should always be discussed with your prescriber or checked in the Patient Information Leaflet, not adjusted based on what you've read online.

What's actually available for weight loss in the UK, and through whom

If weight management is the goal, the two licensed options are Mounjaro and Wegovy. If you are still weighing up whether Ozempic or Mounjaro is better for your situation, the key point is that Ozempic is not a weight-loss alternative; it doesn't carry the licence, and any UK pharmacy offering it specifically for weight loss without a diabetes indication should prompt caution.

On the NHS, Mounjaro became available through a phased rollout following NICE TA1026 (published December 2024). The current NHS criteria are strict: at this stage, a BMI of 40 or above alongside four or more qualifying conditions. Many people also find it helpful to read about how Wegovy and Mounjaro compare across cost, weight-loss results and eligibility before deciding which licensed option to discuss with a prescriber, and Wegovy is available through specialist weight management services under its own NICE guidance, though waiting times are often long.

Private treatment is the route for people who don't meet those NHS thresholds or would prefer not to wait. At nume, a named GPhC-registered Independent Prescriber (not an algorithm) reads your consultation personally. If approved, treatment is dispatched the same day for free next-working-day delivery by DPD, in plain packaging. There are no subscriptions; every repeat order is clinically re-reviewed. For a broader look at all private weight-management options, our treatment overview sets out what's available and who qualifies.

Which of Mounjaro or Wegovy is better suited to you depends on your health history, current medicines and how you responded to any previous treatment. That's not a comparison this page (or any other) can resolve. It's a clinical decision, made with our prescribers.