Mounjaro®
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Start journey Learn moreReading the curves: what the trial evidence and head-to-head data tell you
You found a graph online — here's what it is actually measuring
Picture it: a chart with weeks along the bottom and percentage body-weight change running down the left axis. Two lines descend through the graph, one more steeply than the other. What you're looking at is typically a composite of results from SURMOUNT-1 (tirzepatide) and STEP 1 (semaglutide 2.4mg), both published in the New England Journal of Medicine. The key caveat is that these were separate trials with different participant groups, different durations and modestly different eligibility criteria, so overlaying them into one image is an illustration, not a controlled experiment.
SURMOUNT-1 ran for 72 weeks and randomised 2,539 adults with obesity. Participants on the 15mg tirzepatide dose lost an average of around 20–21% of body weight. STEP 1 ran for 68 weeks with semaglutide 2.4mg, reporting roughly 15% average weight loss. The gap between those two numbers is real, but it cannot be attributed purely to the medicine without accounting for differences in how each trial was designed. A closer look at which performs better requires reading the head-to-head evidence alongside the separate trial figures.
The SURMOUNT-5 trial fills that gap. In a 72-week open-label study of 751 adults with obesity but without diabetes, tirzepatide produced statistically greater average weight loss than semaglutide 2.4mg. That is, as of mid-2026, the most direct evidence behind the graph people share. NICE's appraisal of tirzepatide (TA1026) noted indirect comparisons also favour tirzepatide, while acknowledging that network comparisons carry uncertainty.
Where Wegovy 7.2mg changes the picture
The graph you've seen probably doesn't include the newest data. In January 2026, a higher Wegovy maintenance dose of 7.2mg was approved by the MHRA. Trial results at this dose reported approximately 20.7% average weight loss over 72 weeks, which narrows the gap considerably between semaglutide and tirzepatide 15mg. The MHRA then approved a dedicated single-dose 7.2mg pen on 14 April 2026, making the higher dose more practical to administer.
That shifts the comparison. At highest doses the two medicines now produce much closer results on paper. If you want to understand what drives those remaining differences, our Wegovy vs Mounjaro guide covers the dual GIP and GLP-1 receptor activation for tirzepatide versus single GLP-1 activation for semaglutide, the titration schedules, the side-effect profiles at higher doses and individual tolerance, and explains why these become the deciding factors rather than a headline percentage. The dose schedules for both medicines differ meaningfully and that affects how quickly you reach a maintenance level.
Individual response also varies more than any chart can show. Clinical trial averages mask a wide distribution: some people lose considerably more than the mean, others considerably less. The graph is a useful starting point, not a prediction for any individual patient. A prescriber looking at your full health picture gives you something a curve cannot.
Side-by-side numbers: the comparison table
The table below draws on published trial data and regulatory information from the MHRA. Percentages are trial averages at the highest licensed maintenance doses; individual results vary.
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| Average weight loss (highest dose, trial data) | ~20–21% at 15mg (SURMOUNT-1); greater than semaglutide in SURMOUNT-5 | ~15% at 2.4mg (STEP 1); ~20.7% at 7.2mg (MHRA approval data) |
| Highest licensed maintenance dose (UK) | 15mg once weekly | 7.2mg once weekly (approved April 2026) |
| Starting dose | 2.5mg once weekly | 0.25mg once weekly |
| UK licence (weight management) | BMI ≥30, or ≥27 with a weight-related condition | BMI ≥30 (7.2mg pen); ≥27 with a weight-related condition (standard doses) |
| Administration | Once-weekly subcutaneous injection | Once-weekly subcutaneous injection |
Sources: SURMOUNT-1, NEJM; MHRA approval of the 7.2mg Wegovy pen, GOV.UK; NICE TA1026.
Which line on the graph is yours?
Neither medicine is right for everyone. Eligibility, existing conditions, current medicines, lifestyle and personal preference all feed into the decision. If you're weighing cost as well as results, how Wegovy and Mounjaro compare on price is worth reading before you decide. And if Ozempic has come up in your research, it's worth knowing clearly that Ozempic is the semaglutide brand licensed for type 2 diabetes, not weight loss; the distinction between Mounjaro and Ozempic matters for anyone considering their options.
Plenty of people come to this question after a frustrating wait for NHS treatment. If you'd rather not hold on, a private prescription through a GPhC-registered pharmacy like ours is the regulated alternative, with same-day clinical review. Orders placed by 12pm on a working day (useful if you're planning around a Monday after payday, or fitting treatment around a holiday) are dispatched the same day once approved.
Which medicine suits you is a clinical decision our prescribers make with you. Speak to our prescribers through a free consultation and they'll work through both options with your full health picture in front of them. You can also read more about how to choose between Wegovy and Mounjaro before you start.
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