Mounjaro®
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Start journey Learn moreFactors that actually determine which medicine is likely to work better for you
What the head-to-head trial found, and what it did not settle
The most important piece of evidence here is SURMOUNT-5, a 72-week open-label trial published in the New England Journal of Medicine in 2025. It randomised 751 adults with obesity and no diabetes to either tirzepatide (Mounjaro) or semaglutide 2.4mg (Wegovy) and found that tirzepatide produced a greater average reduction in body weight across the full study population. That result is frequently quoted, and it is accurate. What is quoted less often is that a meaningful proportion of participants responded better to semaglutide, and that average trial outcomes do not map neatly onto individual biology.
NICE's appraisal of tirzepatide, TA1026, acknowledges that indirect comparisons generally favour tirzepatide, but also notes that the two medicines have not been compared across every dose combination. Wegovy's newer 7.2mg maintenance dose, approved by the MHRA in January 2026 and available as a dedicated single-dose pen from April 2026, narrowed the gap further. Trials reported roughly 20.7% average weight loss at 7.2mg over 72 weeks, approaching the higher-dose tirzepatide figures. So the picture is shifting.
The short version: at the doses most widely prescribed so far, Mounjaro has shown a larger average effect at population level, a finding we explore in detail for anyone weighing up the two options. At the highest available Wegovy dose, the difference shrinks. And for any given individual, neither average tells the whole story.
Three reasons Wegovy sometimes works better for a specific person
Side-effect tolerance is one of them. Tirzepatide acts on two receptors, GIP and GLP-1; semaglutide acts on GLP-1 alone. That dual mechanism is thought to drive stronger average weight loss, but it can also mean a different (and sometimes less comfortable) side-effect profile for certain people. Gastrointestinal symptoms such as nausea, constipation and reflux are common with both medicines, though the pattern and intensity can differ. A patient who tolerates semaglutide well but struggles to titrate tirzepatide past an early dose may lose more weight on Wegovy simply because they can stay on it.
Medication interactions and practical factors matter too. Tirzepatide may temporarily reduce absorption of oral medicines, including the contraceptive pill, during the first four weeks of treatment and after each dose increase, NHS guidance recommends adding a non-oral contraceptive method during those windows. For some people, that changes the calculation. Wegovy's standard injection also does not carry an equivalent oral-absorption caution, which can be relevant if someone is managing several daily medicines.
Finally, clinical history plays a role. A prescriber assessing a patient with a particular cardiovascular risk profile, or one who is already established on a specific dose of one medicine, will weigh factors that no comparison table can capture. The question of which is better does not have a single answer independent of the person asking it.
Comparing the two medicines side by side
The table below draws on data from SURMOUNT-1, STEP 1, SURMOUNT-5 and the NICE appraisals. All figures are from clinical trials under supervised conditions alongside lifestyle changes, real-world results vary.
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Mechanism | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist |
| Average weight loss (main trial, 2.4mg / 15mg) | ~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 |
| Head-to-head result | Greater average loss vs semaglutide 2.4mg (SURMOUNT-5, NEJM 2025) | 7.2mg dose narrows the gap significantly |
| Once-weekly injection | Yes (KwikPen, pre-filled | Yes) pre-filled pen; 7.2mg now available as single-dose pen |
| NICE recommendation | TA1026 (published Dec 2024); BMI ≥35 + ≥1 comorbidity (NHS route) | TA875 (published Mar 2023); BMI ≥35 within specialist services (NHS route) |
| Oral contraceptive absorption caution | Yes, add non-oral method for 4 weeks at start and after each dose increase | No equivalent caution identified in NHS guidance |
For a deeper look at how costs compare alongside these clinical differences, our cost comparison page sets out what a full course of each medicine typically involves financially.
How a prescriber actually decides, and what happens at your consultation
No article, including this one, can tell you which medicine is right for you. What a prescriber does is read your medical history, current medicines, BMI, any relevant conditions, and your own priorities, then work through the options with you. That conversation might take ten minutes, or it might involve a follow-up. It cannot be replaced by a table.
Our clinical team at nume approaches this as a genuine clinical assessment, not a box-ticking exercise. Order by midday on a working day and your consultation is reviewed the same day, one of our GPhC-registered prescribers reads it personally. Plenty of people submit theirs during a lunch break and have a decision before they pick the kids up from school.
If you are transferring from one medicine to the other, or wondering whether a different dose would perform better, those are exactly the questions to put in your consultation. You can also read more about the biological reasons behind tirzepatide's stronger average results before you do, or read more about the specific evidence behind Wegovy's performance. The right starting point is a free consultation, and which medicine suits you is a clinical decision our prescribers make with you.
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