Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow the evidence compares — and what it means if you're already on semaglutide
What the SURMOUNT-5 trial found when tirzepatide went head-to-head with semaglutide
For years, comparing tirzepatide and semaglutide relied on indirect analysis across separate trials. That changed with SURMOUNT-5, published in the New England Journal of Medicine in 2025. The trial enrolled 751 adults with obesity and no diabetes, randomised them to either tirzepatide or semaglutide 2.4mg, and followed them for 72 weeks. Tirzepatide produced greater average weight reduction across the study period. NICE's appraisal of tirzepatide (TA1026) noted that indirect comparisons also favour tirzepatide, and described the evidence base as robust enough to recommend it within the NHS for eligible adults.
Why the difference? Tirzepatide activates two gut-hormone receptors simultaneously (GIP and GLP-1) while semaglutide acts on GLP-1 alone. That dual action appears to produce stronger appetite suppression and a more pronounced effect on gastric emptying in most people. Neither mechanism is better in every individual, but the population-level trial data consistently shows tirzepatide ahead on average weight loss figures.
One important context: Wegovy's 7.2mg dose, approved by the MHRA in January 2026, narrows that gap. Trials at 7.2mg reported approximately 20.7% average weight loss over 72 weeks, approaching tirzepatide 15mg results. If you've only ever been on 2.4mg semaglutide, your prescriber may consider whether a dose increase is appropriate before a full switch.
| Factor | Semaglutide (Wegovy injection) | Tirzepatide (Mounjaro) |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | Dual GIP and GLP-1 receptor agonist |
| Trial average weight loss (maintenance dose, 72 weeks) | ~15% at 2.4mg (STEP 1); ~20.7% at 7.2mg | ~20–21% at 15mg (SURMOUNT-1) |
| Head-to-head result | Lower average loss vs tirzepatide (SURMOUNT-5, NEJM 2025) | Greater average loss (SURMOUNT-5, NEJM 2025) |
| 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 |
| Side-effect profile | GI-led (nausea, vomiting, diarrhoea); generally settles | GI-led (similar profile); generally settles |
| NICE recommendation | TA875 (within specialist services, max 2 years | TA1026) phased NHS rollout from 2025 |
What actually changes when you switch, and what stays the same
The side-effect profile of the two medicines is broadly similar. Both cause GI symptoms most commonly (nausea, loose stools, reduced appetite) and both tend to peak around dose increases before settling. If you tolerated semaglutide reasonably well, that's useful information for your prescriber, but it doesn't mean the switch will be identical. Tirzepatide is a different molecule acting on an additional receptor, and some people find the transition brings a new wave of nausea, particularly at higher doses.
It's understandable to feel some uncertainty here. Moving between treatments when one has already taken effort to establish is not a trivial thing, and the honest answer is that individual responses vary enough that no one can predict your exact experience in advance.
The dosing schedule is also different, and this matters practically. Tirzepatide starts at 2.5mg regardless of what dose of semaglutide you were on, the starting dose exists to allow your system to adjust, not because 2.5mg is where the therapeutic effect sits. Your prescriber will decide how to time the transition and which dose to start on; the dosing considerations for switching are a clinical judgement, not a straight conversion. For a broader look at how the two medicines compare across all factors, the tirzepatide vs semaglutide guide covers the full picture.
Which people might be candidates for switching, and the questions a prescriber will ask
Switching is most commonly discussed when someone has reached the maintenance dose of semaglutide, achieved some weight loss but less than hoped, and has no clinical reason to avoid tirzepatide. It may also be relevant if supply issues have disrupted treatment, or if a prescriber judges that the dual-agonist mechanism is likely to suit a particular metabolic profile better.
Switching is not appropriate simply because tirzepatide scored higher in a clinical trial. Population averages don't determine individual outcomes. A prescriber considering a switch will typically want to know: how long you've been on semaglutide, what dose you reached, how much weight you've lost, how you tolerated it, and what your current health picture looks like. People who responded well to semaglutide but want to trial a higher ceiling of effect are different clinically from people who had poor tolerance and are looking for an alternative.
If you're thinking about this the other way around (moving from Mounjaro back to semaglutide) the switching from Mounjaro to semaglutide page addresses that direction separately. For detail on the reverse of this specific journey, switching from Wegovy to tirzepatide sets out the practical steps our prescribers follow.
Ozempic (also semaglutide) is licensed for type 2 diabetes, not weight management. If you've been prescribed Ozempic for diabetes, that's a different clinical context entirely; see the Mounjaro vs Ozempic comparison for more on that distinction. Similarly, cost context between the two treatments is covered in how much Wegovy costs compared to Mounjaro, which may help frame a switch decision from a practical standpoint.
Which option suits you is a clinical decision our prescribers make with you. Speak to our prescribers through a free consultation, every application is reviewed personally, the same day, by a GPhC-registered Independent Prescriber, and you can verify our pharmacy on the GPhC register (9012878) before you begin.
Looking to start your weight loss journey?
Take a quick eligibility quiz to explore your options and see how we can support you.