Mounjaro®
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Start journey Learn moreWhat the trial evidence and head-to-head data actually show
The SURMOUNT-5 result: what a direct comparison found
The clearest evidence comes from SURMOUNT-5, a 72-week open-label trial published in the New England Journal of Medicine in 2025. It randomised 751 adults living with obesity but without type 2 diabetes to either tirzepatide or semaglutide 2.4 mg, the first properly powered head-to-head study of this kind. Tirzepatide produced meaningfully greater average weight reduction. NICE's committee, reviewing both medicines, noted that indirect comparisons also favour tirzepatide, and this was reflected in their appraisal of tirzepatide, NICE TA1026, published in December 2024.
The reason usually offered for the gap is mechanistic. Mounjaro activates two gut-hormone receptors simultaneously (GIP and GLP-1) whereas Wegovy targets GLP-1 alone. Whether that dual action is the full explanation is still an active area of research, but the mechanism difference between the two medicines is real and measurable.
One important nuance: the SURMOUNT-5 comparison used semaglutide at its then-standard 2.4 mg maintenance dose. If you want to understand how the two medicines stack up across doses and settings, our overview of Wegovy compared to Mounjaro sets out the picture in full. The picture may shift slightly as the newer 7.2 mg Wegovy dose becomes more widely used in clinical practice, trials at that higher dose reported average losses of around 20.7% over 72 weeks, which narrows the gap with tirzepatide's top dose considerably.
Putting the headline numbers side by side
The table below draws on published trial data. These are group averages from specific trial populations and should not be read as predictions for any individual.
| Medicine | Trial | Duration | Average weight loss (highest dose) | Source |
|---|---|---|---|---|
| Tirzepatide (Mounjaro) 15 mg | SURMOUNT-1 | 72 weeks | ~20–21% | NEJM 2022 |
| Semaglutide 2.4 mg (Wegovy) | STEP 1 | 68 weeks | ~15% | NEJM 2021 |
| Semaglutide 7.2 mg (Wegovy) | Phase 3 data | 72 weeks | ~20.7% | MHRA approval, April 2026 |
| Tirzepatide vs semaglutide 2.4 mg (direct) | SURMOUNT-5 | 72 weeks | Tirzepatide greater | NEJM 2025 |
The full side-by-side overview of Wegovy and Mounjaro covers eligibility, dosing schedules and NHS access alongside the efficacy data, if you want the broader picture.
Which medicine suits which person: the clinical factors that matter
Effectiveness in a trial population is only part of the story. In practice, several things shape which medicine a prescriber is likely to recommend.
Tolerability varies between people. Both medicines carry a GI-led side-effect profile (nausea, loose stools, slowed digestion) most noticeable in the early weeks of treatment. Some people tolerate one better than the other, and that is not predictable from the trial averages. The NHS medicines page for tirzepatide and the equivalent for semaglutide set out the respective profiles clearly.
Route and format matter too. Mounjaro is a once-weekly injection; Wegovy is also once-weekly by injection, though the newly licensed Wegovy tablet (oral semaglutide, approved by the MHRA in June 2026) offers a needle-free daily option for those who prefer not to inject. If that distinction is relevant to you, the detailed efficacy comparison explores it further.
Existing conditions, other medicines, and contraceptive considerations all feed into the decision. For tirzepatide specifically, anyone taking an oral contraceptive pill should add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because absorption of the pill may be reduced. NHS England's guidance on weight-management injections covers this clearly, and it is something a prescriber will go through with you.
Cost is sometimes a deciding factor too. The cost comparison between Wegovy and Mounjaro sets out the private-market context honestly, including what changed after Eli Lilly revised Mounjaro's UK list price in September 2025.
A note on Ozempic: not the same as Wegovy
Ozempic contains the same molecule as Wegovy (semaglutide) but it is licensed in the UK for type 2 diabetes management, not for weight loss. The doses differ and the licence differs. Prescribing it for weight loss outside its licensed indication is not appropriate, and it is not something a responsible UK prescriber would do routinely. The comparison of Mounjaro and Ozempic explains the distinction in full. If weight management is your goal, the relevant medicines are Mounjaro and Wegovy.
Which of the two is right for you depends on your health history, your current medicines, your starting weight and your preferences, not on the trial headline alone. That is exactly the conversation a prescriber at nume (sorry, at nume) will have with you. Speak to our prescribers by starting a free consultation, and let the clinical picture lead.
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