The Key Differences Between Ozempic and Mounjaro for Weight Loss

The decision you are actually facing: diabetes medicine vs weight-loss medicine

Before comparing anything else, it helps to be clear about what each product is authorised to treat. Mounjaro is a dual GIP and GLP-1 receptor agonist, it activates two separate gut-hormone pathways involved in appetite regulation and blood-sugar control. The NHS medicines page for tirzepatide confirms it is licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 or above if a weight-related condition such as high blood pressure or pre-diabetes is present. Ozempic, by contrast, is semaglutide in a formulation and at doses specifically authorised for type 2 diabetes, not weight loss. The NHS medicines page for semaglutide makes that distinction clear. Prescribing Ozempic for weight loss in someone without diabetes would be off-label use, outside its UK licence. If your goal is weight management, Mounjaro is a licensed option; Ozempic, in its current authorised form, is not the route. The weight-loss version of semaglutide carries a different brand name (Wegovy) and you can read about how Mounjaro and Wegovy compare separately. If you want to go deeper on how the two medicines sit apart from each other before reading further, our page covering the difference between Ozempic and Mounjaro sets out the key distinctions in full. Understanding that boundary is the first step in any decision.

Mechanism, trial evidence and what the numbers actually show

Because Mounjaro works on two receptors and Ozempic (like Wegovy) works on one, the clinical results have tended to differ. In the SURMOUNT-1 trial, adults treated with tirzepatide 15mg saw an average body-weight reduction of around 20–21% over 72 weeks, published in the New England Journal of Medicine. The STEP 1 trial for semaglutide 2.4mg (the Wegovy dose, not Ozempic's dose) showed around 15% average reduction over 68 weeks. Ozempic is used at lower doses calibrated for blood-sugar management rather than maximum weight loss, so the direct comparison is not straightforward. The only head-to-head data between tirzepatide and semaglutide at weight-loss doses comes from the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025: over 72 weeks, tirzepatide produced greater average weight reduction than semaglutide 2.4mg. These are group averages from clinical trials, not guarantees for individuals. A more detailed breakdown of where the two medicines sit against each other is covered in our page on Mounjaro versus Ozempic, and for a side-by-side look at how the two products compare across licensing, dosing and trial results, our page on the Mounjaro and Ozempic difference walks through each factor in turn. Individual response varies, and no prescriber can tell you in advance exactly how your body will respond.

Side-effect profiles: similar families, some differences in detail

Because both medicines slow gastric emptying and reduce appetite through related gut-hormone pathways, their side-effect profiles overlap considerably. Nausea, loose stools, constipation, indigestion and fatigue are reported with both. These effects are generally most noticeable after starting treatment or after a dose increase, and they tend to settle within days to a couple of weeks for most people. The differences worth knowing are in the specifics. Tirzepatide activates GIP receptors in addition to GLP-1 receptors, which may account for some variation in the side-effect experience between individuals, though head-to-head safety comparisons are limited. One important practical note: the NHS advises that women taking oral contraceptive pills should add a non-oral method of contraception for the first four weeks of tirzepatide treatment and for four weeks after each dose increase, because absorption of the pill may be reduced. The same evidence base does not exist for semaglutide. The NHS England guidance on weight-management injections covers this and other practical points. For any side effect that feels severe or persistent (especially significant stomach pain) you should contact a healthcare professional promptly. Suspected side effects can also be reported at the MHRA's Yellow Card scheme.

A factual comparison at a glance

Figures from the SURMOUNT-1 trial (New England Journal of Medicine) and NICE technology appraisal TA1026. Individual results vary.

If you are weighing up Mounjaro against the weight-loss version of semaglutide rather than the diabetes version, the Mounjaro vs Wegovy comparison covers that ground directly. And if cost is a factor in your thinking, our page on why Wegovy tends to be priced differently from Mounjaro explains what drives those differences.

At nume, our prescribers dispense Mounjaro and Wegovy for weight management, both are UK-licensed for that purpose. Ozempic is not something we prescribe for weight loss, because it is not licensed for it. Which of the two licensed options fits your situation is a clinical decision our prescribers make with you, based on your health history, your BMI and what matters most to you. You can explore your options or start a free consultation at any point.