Mounjaro®
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Start journey Learn moreWhat the trial data actually shows when you put semaglutide and tirzepatide side by side
The head-to-head trial that settled the headline question
For years, comparisons between semaglutide and tirzepatide relied on indirect evidence — placing results from separate trials alongside each other and hoping the populations were similar enough to draw conclusions. That changed with SURMOUNT-5, a direct head-to-head trial published in the New England Journal of Medicine in 2025. It randomised 751 adults with obesity but without type 2 diabetes to either tirzepatide (titrated to the highest tolerated dose, up to 15 mg weekly) or semaglutide 2.4 mg weekly, and followed them for 72 weeks.
Tirzepatide produced greater average weight reduction across the trial. At 15 mg, tirzepatide had already shown around 20–21% average body-weight loss in SURMOUNT-1, while semaglutide 2.4 mg showed approximately 15% in the STEP 1 trial. The SURMOUNT-5 head-to-head confirmed that gap under controlled conditions. NICE's appraisal of tirzepatide (TA1026) also acknowledged that indirect comparisons favoured tirzepatide over semaglutide 2.4 mg in terms of average weight reduction.
So if you are asking whether semaglutide is more effective than tirzepatide, the current evidence says it is not, on average. But averages cover a wide range of individual outcomes, and the story doesn't end there.
Where semaglutide narrows or closes the gap
Two things complicate the straightforward reading. First, the 7.2 mg semaglutide dose. The MHRA approved a higher Wegovy maintenance dose in January 2026, and a dedicated single-dose 7.2 mg pen followed in April 2026, one pre-set weekly injection for adults with a BMI of 30 or above. Trials at that dose reported approximately 20.7% average weight loss over 72 weeks, approaching the results seen with tirzepatide 15 mg. That narrows the gap considerably, though a direct comparison at those ceiling doses has not yet been published. You can read more about how the two medicines compare on our Wegovy vs Mounjaro comparison page.
Second, individual response. Some people lose substantially more weight on semaglutide than others lose on tirzepatide at equivalent doses; biology, genetics, gut-hormone profiles and tolerability all play a role. A trial average tells you about a group. It says less about any one person sitting at a specific dose on a specific week. The NHS medicines page for semaglutide and the equivalent tirzepatide page both set out the clinical context clearly.
How the two medicines differ in mechanism, schedule and licensed eligibility
Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist, it activates two gut-hormone pathways simultaneously. Semaglutide (Wegovy, injectable) works on the GLP-1 pathway alone. Whether the dual mechanism explains tirzepatide's numerical advantage in trials is an active area of research, but the practical reality is that tirzepatide is currently the only dual-agonist weight-loss medicine licensed in the UK.
| Factor | Tirzepatide (Mounjaro) | Semaglutide (Wegovy injection) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 agonist | GLP-1 agonist |
| Average weight loss in trials | ~20–21% at 15 mg (SURMOUNT-1, NEJM) | ~15% at 2.4 mg (STEP 1, NEJM); ~20.7% at 7.2 mg |
| UK licensed strengths | 2.5, 5, 7.5, 10, 12.5, 15 mg | 0.25 mg up to 2.4 mg; 7.2 mg (April 2026) |
| NICE recommendation threshold (BMI) | ≥35 + ≥1 comorbidity (TA1026) | ≥35 + ≥1 comorbidity, specialist service, max 2 years (TA875) |
| Administration | Once-weekly subcutaneous injection | Once-weekly subcutaneous injection |
| Side-effect profile | GI-led: nausea, diarrhoea, constipation | GI-led: nausea, vomiting, diarrhoea |
Both require titration by a prescriber and are black-triangle medicines under additional MHRA monitoring. Neither Ozempic nor Rybelsus is licensed for weight management: Ozempic (injectable semaglutide) and Rybelsus (oral semaglutide tablets at 3, 7 and 14 mg) are both licensed specifically for type 2 diabetes. Readers looking for a weight-loss medicine should not be redirected toward those products. For a deeper look at the safety profiles of each, our page on whether semaglutide is safer than tirzepatide covers that question separately.
Which one might be right for you, and how that decision is made
Cost sometimes features in this decision. Tirzepatide's UK list price rose significantly from September 2025, and private monthly costs can differ between the two medicines depending on dose and provider. If you want to understand the pricing difference before starting, our page on why Wegovy is typically priced lower than Mounjaro explains the background. What matters equally, though, is clinical suitability: your medical history, any medicines you currently take, and your personal priorities around injection frequency, dose ceiling and tolerability all shape which option a prescriber would favour.
Some patients have tried one medicine and are curious about switching, and anyone wondering whether Wegovy is less effective than Mounjaro for their situation will find that question worth discussing with a prescriber who can review their treatment record. That is a decision to avoid making on the basis of headline trial figures alone, particularly for anyone who has considered mixing Wegovy and Mounjaro, which is not something a prescriber would recommend. Our clinical team reviews every consultation personally. There is no algorithm involved, no automated approval, and no repeat dispensed without a fresh clinical look at your case. If you are ready to explore which option suits your situation, start your free consultation and a prescriber will work through the evidence with you directly.
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