Mounjaro®
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Start journey Learn moreMounjaro versus Wegovy: what the trial data, side-effect profiles and practical differences actually show
You've been on Mounjaro for a few months and something isn't sitting right
Maybe the nausea has been persistent longer than expected. Maybe a new prescription means your prescriber wants to reconsider your options. Or perhaps you've read that Wegovy now comes in a 7.2mg dose and you're wondering whether it closes the gap. Whatever the reason, the question our prescribers hear regularly is: does switching actually make sense?
The honest answer is: sometimes yes, sometimes no, and the deciding factors are clinical. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist (it activates two appetite-regulating pathways simultaneously) while Wegovy (semaglutide) targets only the GLP-1 receptor. That mechanistic difference partly explains why the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, found greater average weight reduction with tirzepatide than with semaglutide 2.4mg over 72 weeks in adults with obesity. A detailed side-by-side look at both medicines sets out those numbers in full.
But average trial results describe populations, not individuals. Some people lose more on semaglutide than they did on tirzepatide. Tolerability matters enormously too. If the gastrointestinal side effects of Mounjaro haven't settled after a dose increase, a semaglutide-based medicine may suit your system better. That's a conversation for a prescriber, not a product comparison page.
What the evidence shows when you put them side by side
The table below summarises the key factual differences between the two medicines as they stand in the UK today.
| Feature | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| Average weight loss in pivotal trial | ~20–21% at 15mg over 72 weeks (SURMOUNT-1, NEJM) | ~15% at 2.4mg over 68 weeks (STEP 1, NEJM) |
| Higher-dose option | Up to 15mg weekly | Up to 7.2mg weekly (MHRA-approved, April 2026); ~20.7% average loss reported at this dose |
| UK licence (weight management) | BMI ≥30, or ≥27 with ≥1 weight-related condition | BMI ≥30, or ≥27 with ≥1 weight-related condition (7.2mg pen: BMI ≥30 only) |
| Contraception note | Add a non-oral method for 4 weeks when starting and after each dose increase | No equivalent evidence of reduced oral contraceptive absorption |
| Storage | Refrigerated; limited room-temperature window per leaflet | Refrigerated; limited room-temperature window per leaflet |
Sources: SURMOUNT-1, NEJM; STEP 1, NEJM; MHRA approval of the 7.2mg Wegovy pen, April 2026.
The 7.2mg Wegovy dose narrows the average-loss gap considerably. It doesn't close it entirely based on current data, but it makes the comparison less clear-cut than it was two years ago. How tirzepatide and semaglutide work differently at a molecular level is explained in more depth if the mechanism matters to your decision.
Practical reasons a prescriber might consider a switch
There are legitimate clinical reasons to move from one medicine to the other in either direction. Switching from Mounjaro to Wegovy might be considered if: side effects on tirzepatide have been difficult to manage despite a slow titration; a new medication interaction needs accounting for; or a prescriber believes the single-pathway GLP-1 approach is better suited to a particular clinical profile. The full clinical guidance on how switching works in practice covers the process in detail, including what dose to restart on.
It's equally worth knowing that switching back is possible if Wegovy doesn't deliver as hoped. What that return journey looks like is a question prescribers field fairly regularly.
One practical note before a switch: if you take an oral contraceptive and you're moving to Mounjaro, NHS England's guidance on weight-management injections recommends using an additional non-oral method for the first four weeks and after each dose increase — a detail that catches people out. That's the kind of thing a prescriber running through your medical history will flag before any change takes effect.
A word on cost: a like-for-like price comparison between the two medicines is useful context, though after the September 2025 Lilly list-price rise, private monthly costs for both medicines now sit in a broadly similar range by dose. Price alone is not a reason to switch a medicine that's working.
Which is right for you, and how a prescriber makes that call
No comparison page can answer that. A prescriber reviewing your weight-loss progress, your side-effect history, your current medications and your BMI trajectory can. At nume, that review happens the same day you submit your consultation, a named clinician reads your answers, not software. If a switch is clinically appropriate, they'll confirm which medicine, which starting dose on the new treatment, and what to watch for in the first few weeks.
Both Mounjaro and Wegovy are prescription-only medicines that require a clinical assessment before any prescription is issued. That assessment is free at nume, and it's where a switching decision should begin. Whether switching is clinically appropriate in your situation is worth reading before your consultation if you want to go in prepared. Our clinical team is available to discuss your options, and there's no prescription at the end of the consultation unless the medicine is genuinely suitable for you.
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