Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow the trial evidence compares — and what that means if you're considering the switch
What the published data actually shows about these two medicines
The clearest evidence on how Mounjaro and Wegovy stack up comes from SURMOUNT-5, a 72-week open-label head-to-head trial published in the New England Journal of Medicine in 2025. Among adults living with obesity and no diabetes, tirzepatide (Mounjaro) produced a greater average weight reduction than semaglutide 2.4mg (Wegovy) over the trial period. NICE's appraisal of tirzepatide (TA1026) noted that indirect comparisons also favour tirzepatide, though it acknowledged the evidence base for direct comparison was still developing when the appraisal was published.
Wegovy's position has shifted since then. The MHRA approved a 7.2mg maintenance dose for Wegovy in early 2026, with trial data reporting around 20.7% average weight loss over 72 weeks at that dose, notably closer to tirzepatide's headline figures. So the gap has narrowed. That matters if you're weighing up going from Wegovy to Mounjaro, or vice versa, based purely on efficacy numbers.
Mounjaro's SURMOUNT-1 trial reported average body-weight reductions of around 20–21% at the 15mg maintenance dose over 72 weeks, in a study of 2,539 adults with obesity or overweight and at least one weight-related condition. The full SURMOUNT-1 paper in the NEJM provides the source figures. Neither medicine guarantees any individual a specific result; these are population averages from controlled trials.
The key differences that actually affect the switch
There is a widely held assumption that switching between these two medicines is essentially a like-for-like change, just a different brand. It isn't. The receptor mechanisms differ: Mounjaro activates both GIP and GLP-1 receptors, while Wegovy acts on GLP-1 alone. That difference in mechanism means your body's response to a switch can be unpredictable in the early weeks, and it is also one reason why Rybelsus, despite containing a GLP-1 medicine, is not the same as Mounjaro.
The detailed side-by-side comparison of Wegovy and Mounjaro on this site covers tolerability profiles, but the practical summary is that the side-effect landscape is broadly similar (nausea, changes in appetite, gastrointestinal symptoms) and most people find these settle as the body adjusts. The timeline for that adjustment after a switch is not identical to the timeline at first initiation.
Dosing schedules are also structured differently. Both are once-weekly subcutaneous injections, but the titration steps and maintenance doses don't map neatly onto each other. A prescriber will decide the starting dose for the new medicine based on where you are clinically, not simply by matching milligrams. The NHS's patient information on tirzepatide and its equivalent for semaglutide give plain-language summaries of each medicine's profile.
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| UK licence (weight) | BMI ≥30, or ≥27 with ≥1 weight-related condition | BMI ≥30, or ≥27 with ≥1 weight-related condition |
| Average weight loss (phase 3, 72 weeks) | ~20–21% at 15mg (SURMOUNT-1, NEJM) | ~15% at 2.4mg (STEP 1, NEJM); ~20.7% at 7.2mg |
| Head-to-head result | Greater average loss in SURMOUNT-5 (NEJM 2025) | 7.2mg narrows the gap considerably |
| Injection frequency | Once weekly | Once weekly |
| NICE appraisal | TA1026 (December 2024) | TA875 (March 2023) |
Why someone might switch, and why the direction of travel matters
People ask about whether you can go from Mounjaro to Wegovy for several practical reasons: cost, availability, tolerability issues on the current medicine, or a clinical recommendation from their prescriber. Occasionally the question runs the other way, and if you are established on Mounjaro and wondering what a move to Wegovy would involve practically, the guide to switching from Mounjaro to Wegovy walks through the key considerations in detail. Both directions are legitimate clinical conversations.
What a prescriber needs to know before approving a switch includes: how long you've been on the current medicine, your current dose, how much weight you've lost, any side effects you've experienced, and whether the reason for switching is clinical or logistical. Transfer patients at nume are asked to provide evidence of their current treatment; this is a GPhC-registered pharmacy and clinical corners don't get cut. You can read more about our clinical team's approach on the prescriber profile page.
Cost is sometimes a factor. How the prices of the two medicines compare in the UK depends on dose and provider, and the picture has changed since Eli Lilly revised Mounjaro's list price upward in September 2025. Factoring cost into a switch decision is reasonable; doing it without a clinical conversation is not.
How to approach the switch practically
If you're already on Mounjaro and want to move to Wegovy, or the reverse, the process at nume's treatment page starts with a free consultation. A prescriber reviews your case (the same day for requests received before 12pm Monday to Friday) and will ask about your current treatment, dose, and reason for switching. The consultation is the mechanism by which a clinical decision gets made; it cannot be skipped or approximated.
There is no universal washout period between the two medicines, but the prescriber will use clinical judgment on timing and starting dose. For a fuller overview of the switch in either direction, the guide to going from semaglutide to tirzepatide covers the Wegovy-to-Mounjaro journey in detail. And if you want to explore available treatments before deciding, the treatment overview sets out all options clearly. Which medicine suits you is a clinical decision our prescribers make with you.
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