Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow a switch between these two medicines actually works, and what the evidence says about each
The misconception: switching is just a medicine name change
Most people who ask about switching assume the main question is which pen to order next. The bigger question is whether the switch is clinically warranted, and if so, how to manage the transition safely. Wegovy (semaglutide) and Mounjaro (tirzepatide) work differently at the receptor level. Wegovy activates GLP-1 receptors; Mounjaro activates both GLP-1 and GIP receptors, making it the only dual-agonist weight-loss medicine currently licensed in the UK. That difference in mechanism means your body's response to one is not a reliable guide to how it will respond to the other.
There is no licensed cross-titration schedule that maps, say, 1.7mg semaglutide to a specific tirzepatide starting point. A prescriber will generally assess your current progress, side-effect history, and any conditions you have before deciding where to begin the new medicine. Jumping straight to a high dose of the replacement is not routine practice. The practical detail for dosing and timing lives in each medicine's Patient Information Leaflet and in your prescriber's guidance, not on switching guides found online. You can read more about what the process looks like in practice on the switching between Mounjaro and Wegovy page.
Both medicines carry a Black Triangle (▼) status with the MHRA, meaning they are subject to additional monitoring. A switch is a clinical moment, not an admin task.
What the trial evidence actually shows about each medicine
Understanding what each medicine has demonstrated in trials is useful context, though results from a population tell you nothing definitive about your individual response.
| Feature | Mounjaro (tirzepatide) | Wegovy (semaglutide 2.4mg) |
|---|---|---|
| Receptor targets | GLP-1 and GIP (dual agonist) | GLP-1 only |
| Average weight loss in trials | ~20–21% at 15mg over 72 weeks (SURMOUNT-1, NEJM) | ~15% at 2.4mg over 68 weeks (STEP 1, NEJM) |
| Head-to-head evidence | Greater average weight reduction than semaglutide 2.4mg (SURMOUNT-5, NEJM 2025) | Wegovy 7.2mg narrows the gap; no head-to-head vs tirzepatide yet at that dose |
| UK licence for weight management | Yes (adults, BMI ≥30 or ≥27 with a weight-related condition) | Yes (same eligibility criteria) |
| Higher-dose option | Up to 15mg per week | Up to 7.2mg per week (MHRA-approved April 2026) |
| NICE recommendation | TA1026, December 2024 | TA875, March 2023 |
The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, found tirzepatide produced greater average weight loss than semaglutide 2.4mg over 72 weeks in adults with obesity and no diabetes. NICE's appraisal of tirzepatide (TA1026) also noted that indirect comparisons favour tirzepatide. That said, Wegovy at 7.2mg is a more recent development, and the gap may narrow at that dose. You can compare the two medicines side by side on the difference between Mounjaro and Wegovy page, or look at the Wegovy vs Mounjaro overview for a broader breakdown.
Common reasons people consider switching, and what the prescriber looks at
A question our prescribers hear regularly is: should I try the other one if this one isn't working? There are a few genuinely different reasons someone might want to switch, and each points the clinical assessment in a different direction.
Some people have plateaued on semaglutide and want to try tirzepatide because the trial data suggests a higher ceiling for weight loss. Others are finding side effects on one medicine more disruptive than they expected and wonder whether the other would suit them better. A smaller group want to move from Mounjaro to Wegovy, sometimes for reasons of supply or because their prescriber believes semaglutide is a better fit for their cardiovascular profile. The considerations around moving from Mounjaro to Wegovy are slightly different from the reverse direction, since the starting-dose logic differs.
What a prescriber looks at: how long you have been on the current medicine, what dose you reached, how much weight you have lost, what side effects you experienced, and any conditions or medicines that interact with the new choice. Oral contraceptive users switching to Mounjaro, for instance, are advised to add a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide may reduce pill absorption, as NHS England's guidance on weight-management injections explains. None of that gets assessed by a checkout form. It gets assessed by a prescriber. You can also read about moving in the other direction on the switching from Mounjaro to semaglutide page.
A word on Ozempic, Rybelsus, and what isn't licensed for weight loss
Switching conversations sometimes bring in Ozempic or Rybelsus. Ozempic is semaglutide, the same molecule as Wegovy, but it is licensed in the UK for type 2 diabetes, not weight management. Rybelsus is oral semaglutide, also licensed for type 2 diabetes only. Neither is a licensed weight-loss medicine, and neither is something a prescriber would offer as a weight-loss switch. If you arrived here from a search about moving from Ozempic, the Ozempic to Mounjaro page covers that ground clearly, as does the Mounjaro vs Ozempic comparison for context.
The licensed options for weight management in the UK are Mounjaro, Wegovy (injection and, from June 2026, the oral tablet), and orlistat. If you're not sure which applies to you, the weight-loss treatment overview is a good place to start. Which medicine suits you is a clinical decision our prescribers work through with you, not one this page can make.
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