Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow Mounjaro and Wegovy starter doses actually compare, and why the numbers don't translate directly
The misconception: that starter doses sit on the same scale
The most common misreading here is that 0.25mg Wegovy and 2.5mg Mounjaro are doing the same job at different concentrations, and that you could convert one to the other with simple arithmetic. They can't. Semaglutide and tirzepatide bind to different receptors, Wegovy acts on a single GLP-1 receptor pathway, while Mounjaro activates both GIP and GLP-1 receptors simultaneously, making it the only dual-agonist weight-loss medicine licensed in the UK. Different mechanisms, different molecular weights, different dose ranges: the numbers are not on the same axis. The question of equivalent dosing between Mounjaro and Wegovy has no clean answer, which is precisely why prescribers don't switch between them using a conversion chart.
What both starter doses share is their purpose: they are tolerability doses. Wegovy begins at 0.25mg and Mounjaro at 2.5mg not because those amounts produce meaningful weight loss, but because they let your body adjust to the medicine's gastrointestinal effects before the dose climbs. The therapeutic work happens later, at maintenance doses. Starting low is how both medicines are designed, it's protocol, not a low-potency phase.
If you're trying to understand what the 0.25mg Wegovy starting point means in practical terms, our page on what 0.25mg Wegovy is equivalent to in Mounjaro covers the receptor-pathway differences in more depth.
What the trial evidence actually shows at each medicine's effective dose
Because the starting doses aren't therapeutic, the more useful comparison is between what each medicine achieves at the doses where it actually works. The SURMOUNT-1 trial, published in the New England Journal of Medicine, recorded average body-weight reductions of around 20–21% over 72 weeks at the 15mg tirzepatide maintenance dose. The STEP 1 trial, also in the New England Journal of Medicine, found approximately 15% average weight loss over 68 weeks with semaglutide 2.4mg. In the SURMOUNT-5 head-to-head trial (72 weeks, published in the NEJM in 2025), tirzepatide produced greater average weight reduction than semaglutide 2.4mg in adults with obesity and no diabetes.
These are population averages from controlled trials; individual results vary. A newer 7.2mg Wegovy dose (approved by the MHRA in April 2026) has reported around 20.7% average weight loss, narrowing the gap. For a fuller look at how costs map alongside these differences, our page on tirzepatide versus semaglutide costs puts both in context. And the detailed mechanism-and-results picture sits on our Wegovy vs Mounjaro comparison page.
| Factor | Wegovy (semaglutide) | Mounjaro (tirzepatide) |
|---|---|---|
| Receptor pathway | GLP-1 agonist | Dual GIP and GLP-1 agonist |
| Starting dose | 0.25mg weekly | 2.5mg weekly |
| Standard maintenance dose | 2.4mg weekly | Up to 15mg weekly |
| Average weight loss (pivotal trial) | ~15% at 2.4mg over 68 weeks [STEP 1, NEJM] | ~20–21% at 15mg over 72 weeks [SURMOUNT-1, NEJM] |
| UK licence for weight management | Yes (BMI ≥30, or ≥27 with a weight-related condition) | Yes (BMI ≥30, or ≥27 with a weight-related condition) |
| Dose conversion between the two | Not clinically established; no validated equivalence scale | |
Who each medicine is licensed for, and what that means in practice
Both medicines share the same headline eligibility: adults with a BMI of 30 or above, or 27 and above when at least one weight-related condition is present (such as high blood pressure, prediabetes, high cholesterol, or obstructive sleep apnoea). Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. Neither medicine is licensed for under-18s, and neither is recommended during pregnancy, while breastfeeding, or when actively trying to conceive. Those are the boundaries the SmPCs set; a prescriber then assesses the full clinical picture before making a recommendation.
The practical question of which to start is shaped by factors a dose comparison can't settle: your medical history, any medicines you currently take, whether you're on oral contraception (tirzepatide may reduce pill absorption in the early weeks, so a non-oral method is typically advised), and your own preferences around how treatment works. Our page on the Wegovy 0.25mg and Mounjaro comparison explores the eligibility angle further, and our clinical team is well placed to walk through those factors with you. NICE's published guidance on tirzepatide (TA1026) and on semaglutide (TA875) set out the formal NHS criteria for each.
Switching between Wegovy and Mounjaro: what happens at the dose level
For people already on one medicine who are curious about the other, the absence of an equivalence table matters even more. There is no authoritative dose-conversion guide for moving from Wegovy to Mounjaro or vice versa, because the medicines have never been validated as interchangeable. A prescriber managing a switch would make a clinical judgement about where to start on the new medicine's own titration schedule, taking into account current progress, tolerability and medical history. Our page covering Mounjaro-to-Wegovy dose conversion is honest about those limits.
If you're considering a switch or want to understand what the 1mg Wegovy phase looks like relative to Mounjaro's middle doses, our 1mg Wegovy equivalent page and the 5mg Mounjaro equivalent page both explain why mid-ladder comparisons face the same fundamental problem as the starting-dose ones. Worth knowing before you draw conclusions from a number alone.
Which medicine suits you is a clinical decision our prescribers make with you, based on your full picture. You can check your eligibility and start a free consultation to get that conversation going.
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