Thinking about switching from Mounjaro to Ozempic for weight loss? Here's what the evidence actually shows

The myth: Ozempic is interchangeable with Wegovy for weight loss

This is the misconception that sends a lot of people down the wrong path. Ozempic and Wegovy both contain semaglutide (same molecule, same manufacturer (Novo Nordisk)) but they carry different UK licences for different doses and different patient groups. Ozempic (0.5 mg, 1 mg, 2 mg) is authorised by the MHRA for type 2 diabetes. Wegovy (starting at 0.25 mg, escalating to 2.4 mg, with a 7.2 mg dose now also approved) is authorised for weight management in adults with a BMI of 30 or above, or 27 and above with a weight-related condition. The difference between Mounjaro and Ozempic goes further than branding: the licensed dose for weight loss in Wegovy is substantially higher than the doses used in Ozempic for diabetes. A prescriber writing Ozempic for weight loss would be prescribing outside its UK licence, which is why you will not find a responsible UK pharmacy doing it. The MHRA is unambiguous on this point, as is NHS guidance on semaglutide. If someone online is offering Ozempic for weight loss without asking about a diabetes diagnosis, that is a red flag worth taking seriously.

What the head-to-head evidence shows when comparing tirzepatide and semaglutide for weight loss

The honest comparison, then, is between Mounjaro (tirzepatide) and Wegovy (semaglutide). The SURMOUNT-5 trial (a direct, open-label head-to-head study in 751 adults with obesity but without diabetes, published in the New England Journal of Medicine in 2025) found that tirzepatide produced greater average weight reduction over 72 weeks than semaglutide 2.4 mg. Separately, SURMOUNT-1 reported around 20–21% average body-weight reduction at tirzepatide 15 mg over 72 weeks, while STEP 1 reported approximately 15% average reduction with semaglutide 2.4 mg over 68 weeks. The newer 7.2 mg Wegovy dose, approved by the MHRA in January 2026 and available as a dedicated single-dose pen from April 2026, narrows that gap, trials reported around 20.7% average weight loss at 72 weeks. Numbers from different trials should be read carefully: populations, run-in periods and baseline weights vary. If you want to understand more about the difference between Wegovy and Mounjaro, that page sets out how the two medicines compare before you look at the broader trial data. NICE's appraisal of tirzepatide (TA1026) also notes that indirect comparisons favour tirzepatide, though it stops short of declaring one definitively superior for every patient, because individual response matters as much as average trial results.

Switching from Mounjaro to Wegovy: when does it make clinical sense?

There are a few genuine reasons a prescriber might consider moving someone from tirzepatide to semaglutide, or the other direction. Side-effect profile is one: the two medicines share a broadly similar GI pattern (nausea, loose stools, reflux) but individual tolerance varies, and what one person finds manageable can be genuinely difficult for another. Supply, clinical response, and changes in a patient's health picture (a new diagnosis, a contraindication emerging) are others. What switching is not, clinically, is a shortcut or an upgrade. Switching from Mounjaro to Wegovy involves retitrating the new medicine carefully (you do not simply transfer dose-for-dose) and that process needs prescriber oversight. If you are currently on Mounjaro and it is working, there is rarely a clinical reason to switch without one. If you have been reading about switching from semaglutide to tirzepatide and want to understand the direction more common in clinical practice, that page covers the practicalities. The question our prescribers are best placed to answer is not "which is better" in the abstract, but what is right for your history, your current dose, and your goals. You can explore how Wegovy and Mounjaro compare for weight loss in more depth if you want the fuller picture before your consultation.

What IS licensed for weight loss in the UK, and how to access it properly

To be direct: if you arrived here hoping to switch from Mounjaro to Ozempic for weight loss, the licensed route is either to stay on Mounjaro or to switch to Wegovy, not Ozempic. Both Mounjaro and Wegovy are prescription-only medicines, meaning a qualified prescriber must assess your suitability before any treatment begins or changes. At nume, that assessment is carried out by a GPhC-registered Independent Prescriber, a real clinician reading your consultation, not software processing a form. If you are already taking Mounjaro through us, your repeat reviews already build in a clinical check on whether your current treatment is still the right one. If you are new to treatment, or considering a switch from elsewhere, our prescribers weigh up the full picture: BMI, weight-related conditions, previous response to treatment, current medications, and anything that might affect which medicine suits you. Which of these medicines works better for weight loss is a question with a more nuanced answer than most comparison articles suggest, which is exactly why it belongs in a clinical conversation rather than a search result. Which suits you is a clinical decision our prescribers make with you, not a choice to make on the basis of cost or availability alone.