Mounjaro®
Starting from £179.99/mo
Start journey Learn moreMounjaro vs Wegovy: trial results, mechanism and what the numbers mean for you
What the head-to-head trial actually found
The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, is the only randomised head-to-head comparison of tirzepatide and semaglutide 2.4mg for weight management. Over 72 weeks, 751 adults with obesity but without diabetes took one or the other. Tirzepatide produced greater average weight loss — the gap was meaningful rather than marginal. Participants on tirzepatide at the highest tolerated dose lost around 20–21% of body weight on average in SURMOUNT-1 (a separate large trial), while semaglutide 2.4mg participants in STEP 1 lost around 15% on average over 68 weeks, as reported in that NEJM trial paper.
A few things are worth keeping in mind. These are averages across large groups; individual responses vary considerably. SURMOUNT-5 was open-label, meaning participants knew which medicine they were taking, which can influence adherence and reported outcomes. NICE's appraisal of tirzepatide (TA1026) acknowledged that indirect comparisons favour tirzepatide, but stopped short of calling SURMOUNT-5 definitive on its own. The evidence is strong, not simple.
One other development narrows the gap: the MHRA approved a 7.2mg maintenance dose of Wegovy in early 2026, with trials reporting around 20.7% average weight loss over 72 weeks at that dose. That brings semaglutide closer to tirzepatide's headline numbers, though the two medicines are still not identical in effect.
Why the mechanism gap matters, and sometimes doesn't
Mounjaro activates two gut-hormone receptors, GIP and GLP-1. Wegovy activates only GLP-1. Both slow gastric emptying, reduce appetite and affect blood-sugar regulation. The dual action of tirzepatide is the leading explanation for its stronger average performance, and if you're wondering whether Wegovy works like Mounjaro at a mechanistic level, the short answer is that it shares some effects but not all. The NHS tirzepatide page and the NHS semaglutide page describe how each works in plain terms.
In practice, though, mechanism alone doesn't predict how you respond. Some people tolerate one medicine far better than the other, gastrointestinal side effects (nausea, vomiting, diarrhoea, constipation) are the most common issue with both, and they tend to settle as your body adjusts. Others have a health history that makes one more appropriate regardless of the average trial result. A prescriber weighs all of that. The numbers in a trial paper are a starting point for the conversation, not the end of it.
Both medicines are once-weekly subcutaneous injections, both are licensed for adults with a BMI of 30 or above (or 27-plus with a weight-related condition), and both carry a Black Triangle designation reflecting their status as newer medicines under additional MHRA monitoring.
Side-by-side: what the key figures look like in one place
| Feature | Mounjaro (tirzepatide) | Wegovy injection (semaglutide) |
|---|---|---|
| Average weight loss (pivotal trial) | ~20–21% at 15mg over 72 weeks (SURMOUNT-1) | ~15% at 2.4mg over 68 weeks (STEP 1); ~20.7% at 7.2mg over 72 weeks |
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| Dosing range | 2.5mg–15mg, once weekly | 0.25mg–7.2mg, once weekly |
| UK licence (weight management) | Yes (BMI ≥30, or ≥27 with a weight-related condition | Yes) same thresholds |
| NICE recommendation | TA1026 (December 2024) | TA875 (March 2023, max 2 years, specialist services) |
| Head-to-head evidence | SURMOUNT-5 (NEJM 2025): tirzepatide produced greater average weight loss | |
Numbers in this table are drawn from published trial data and NICE appraisals; individual results will differ. More detail on the pricing side of this decision is on our Mounjaro vs Wegovy price comparison page.
How a prescriber at nume thinks through the choice
People often arrive at this question having done a fair amount of reading, which is genuinely useful. Many want to know whether Wegovy works the same as Mounjaro, and others are specifically asking whether Wegovy is as good as Mounjaro given the trial data, while those who have already tried tirzepatide often want to understand whether Wegovy works after Mounjaro if they need to switch. But the data only takes you so far. A prescriber looks at things the trial averages can't capture: your current medicines (some interact differently with each), your GP's records, any history of pancreatitis or thyroid conditions, whether you're using oral contraceptives (tirzepatide specifically can reduce pill absorption in the first four weeks of each dose increase, so an additional method is advised, semaglutide doesn't carry the same evidence of this effect), and frankly, how you feel about injections versus what's available. If you want a focused look at the efficacy question, our page on whether Wegovy works as well as Mounjaro goes into that in more detail.
If you'd like to explore whether either medicine is right for you, the free consultation at nume is the place to start. You don't need a GP referral, there's no waiting list, and our prescribers (you can read about the clinical team here) review your answers the same working day. Questions before you start? The FAQ page covers the most common ones, or get in touch directly. Which medicine suits you is a clinical decision our prescribers make with you, based on your full picture, not the headline from a single trial.
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