Is Mounjaro the Same as Ozempic? No — and the Difference Matters

The myth worth correcting first: Ozempic is not a UK weight-loss medicine

Ask our prescribers what question comes up most weeks and this is it, patients arrive having read about Ozempic online, assuming it is the same as, or interchangeable with, the injection they've been prescribed for weight loss. It isn't. The Ozempic and Mounjaro distinction is a licensing question, not a branding quirk. Ozempic (semaglutide 0.5mg, 1mg and 2mg) is authorised in the UK by the MHRA for the treatment of type 2 diabetes. The NHS semaglutide information page makes this clear: Ozempic is a diabetes medicine. Using it for weight loss in the UK without a diabetes diagnosis would mean obtaining it outside its licensed indication.

Wegovy (also semaglutide, but at a higher 2.4mg weekly maintenance dose and formulated differently) is the product licensed for weight management. Mounjaro (tirzepatide) holds a separate UK licence for weight management. Those are the two medicines a private prescriber in the UK can lawfully assess you for in a weight-loss context. If you've seen Ozempic described as a weight-loss pen on social media, that content was either produced for a different jurisdiction or is simply inaccurate.

This isn't a technicality. It shapes which medicines a regulated UK pharmacy can supply for this purpose, what safety data the prescriber works from, and what clinical monitoring is expected. The relationship between tirzepatide and Ozempic's active ingredient semaglutide goes deeper than the brand names suggest.

How Mounjaro and Ozempic differ in their mechanism

Both medicines slow gastric emptying and act on receptors that regulate appetite and blood-glucose levels. The meaningful difference is in the scope of that action. Ozempic targets one receptor pathway, the GLP-1 receptor. Mounjaro is a dual agonist: it activates both the GLP-1 receptor and the GIP (glucose-dependent insulinotropic polypeptide) receptor simultaneously. This dual action is why tirzepatide is classified separately and why the comparison between Wegovy and Mounjaro (both licensed for weight management) is more clinically meaningful than comparing Mounjaro with Ozempic.

In clinical trials, the difference in receptor coverage translated into a difference in outcomes. SURMOUNT-1, published in the New England Journal of Medicine, reported average body-weight reductions of around 20–21% at the 15mg dose of tirzepatide over 72 weeks. The STEP 1 trial of semaglutide 2.4mg (Wegovy, not Ozempic) reported around 15% average reduction over 68 weeks. SURMOUNT-5, a head-to-head trial published in the New England Journal of Medicine in 2025, compared tirzepatide directly against semaglutide 2.4mg, and tirzepatide produced greater average weight reduction. These figures are from clinical trial populations and won't match everyone's experience, but they are the basis for the comparison.

The question of whether Ozempic performs as well as Mounjaro is complicated by the fact that the approved doses differ substantially between the two products' indications.

Side-effect profiles and what they share

Because both medicines act on the GLP-1 receptor, their side-effect profiles overlap considerably. Nausea, loose stools, constipation, indigestion and fatigue are common to both, particularly when starting or after a dose increase. Injection-site reactions can occur with either. Most gastrointestinal effects settle within a few days to a couple of weeks as the body adjusts.

Pancreatitis is a serious but infrequent side effect flagged for the class. In January 2026, the MHRA issued a Drug Safety Update specifically for GLP-1 medicines, advising patients and clinicians to be alert to severe stomach pain that radiates to the back, with or without vomiting, and to seek urgent medical attention if it occurs. Any suspected side effect from either medicine can be reported via the MHRA Yellow Card scheme.

Contraindications, drug interactions and individual health history affect which medicine is appropriate. Neither should be used in pregnancy, breastfeeding or while actively trying to conceive. Women using oral contraceptives starting Mounjaro are advised to add a barrier method for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide's effect on gastric emptying may reduce the pill's absorption. That specific caution does not apply in the same way to semaglutide. These nuances are exactly why a prescriber's assessment matters.

What the numbers actually show side by side

The table below compares the two products on the facts most readers are looking for. Note that Ozempic's weight-loss figures come from the diabetes trials and are not the basis for a UK weight-management licence.

For a fuller side-by-side look at the two licensed weight-management options, the Wegovy vs Mounjaro comparison is the relevant page, and cost context is covered in our Wegovy vs Mounjaro cost breakdown. If you'd like to explore treatment options with our prescribers, you can start your free consultation today. Which medicine is right for you is a clinical decision, one our prescribers work through with you individually, based on your health history, BMI and goals.