Mounjaro®
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Start journey Learn moreWhat the evidence actually shows when you put semaglutide and tirzepatide side by side
The trial numbers that start the conversation
Three large randomised trials define the evidence base here. STEP 1 (68 weeks, semaglutide 2.4mg) reported an average body-weight reduction of around 15% compared with placebo, as published in the New England Journal of Medicine. SURMOUNT-1 (72 weeks, tirzepatide 15mg) reported average reductions of around 20–21%, roughly a third more. Then SURMOUNT-5 put the two medicines in the same study: adults with obesity but without type 2 diabetes, randomly assigned to tirzepatide or semaglutide 2.4mg, followed for 72 weeks. Tirzepatide came out ahead on average weight loss. The detail behind that head-to-head result matters, because the gap was not uniform across all participants or all doses.
Semaglutide also now has a 7.2mg maintenance dose, approved by the MHRA on 14 April 2026. Trials reported roughly 20.7% average weight loss at 7.2mg over 72 weeks, closer to tirzepatide 15mg than the original 2.4mg data suggested was possible. So the gap between the two medicines is narrowing as both evolve, and if you are trying to work out which of the two is best for you, that newer semaglutide data is worth factoring in. A fuller look at Wegovy versus Mounjaro covers that newer data in more depth.
A head-to-head comparison in plain figures
| Factor | Semaglutide (Wegovy injection) | Tirzepatide (Mounjaro) |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | Dual GIP and GLP-1 receptor agonist |
| Average weight loss (main trial, maintenance dose) | ~15% at 2.4mg (STEP 1, 68 weeks) [NEJM] | ~20–21% at 15mg (SURMOUNT-1, 72 weeks) [NEJM] |
| Higher dose option | 7.2mg pen approved April 2026 (~20.7% in trials) | 15mg is the current maximum licensed dose |
| UK licence (weight management) | BMI ≥30, or ≥27 with ≥1 weight-related condition | BMI ≥30, or ≥27 with ≥1 weight-related condition |
| NICE recommendation | TA875 (max 2 years, specialist weight management service | TA1026 (Dec 2024)) no 2-year cap in the recommendation |
| Dosing format at nume | Once-weekly injection; oral tablet (25mg) also now licensed | Once-weekly injection via KwikPen |
One practical check worth doing now: the NICE tirzepatide appraisal (TA1026) and the NICE semaglutide appraisal (TA875) each set out the eligibility thresholds your GP uses on the NHS. Reading the recommendations chapter of either takes under a minute, and it tells you exactly where you stand for NHS access before you pursue the private route.
Where semaglutide still holds its own
The raw efficacy numbers favour tirzepatide, but that is not the end of the question. Semaglutide's clinical record is longer, STEP 1 was published in 2021, giving real-world pharmacovigilance data a head start. It also holds UK authorisations beyond weight management: the MHRA has approved semaglutide (Wegovy) to reduce major cardiovascular event risk in eligible adults, and in July 2026 granted conditional approval for treating a form of fatty liver disease (MASH). A question that sometimes arises alongside this is whether Wegovy is actually the same as tirzepatide, and the short answer is no, they work through overlapping but distinct mechanisms, which is part of why their licensed indications differ. For someone whose prescriber is weighing up cardiovascular risk alongside weight, that distinction is clinically relevant. Safety comparisons between the two medicines are covered separately, because the tolerability profiles, while broadly similar, have differences worth reading about before you decide.
The side-effect landscape for both is led by gastrointestinal symptoms (nausea, constipation, loose stools, indigestion) most noticeable when starting or moving up a dose. These almost always ease within a couple of weeks. Neither medicine is suitable during pregnancy, breastfeeding, or for anyone actively trying to conceive, and neither is licensed for people under 18. Beyond that, individual health history shapes which is appropriate: a conversation with a prescriber, not a comparison table, is where that gets resolved.
How the prescribing decision actually works at nume
A prescriber at nume reviews every consultation personally, your answers go to a clinician, not a decision algorithm. Our clinical team considers your BMI, any existing conditions, your medication list (relevant because tirzepatide can temporarily reduce absorption of oral contraceptives, which matters for the first four weeks of treatment and after each dose increase), and your own preferences. Some people find an injectable routine straightforward; others want to explore whether the oral semaglutide tablet, licensed in the UK since June 2026, suits them better. Check your eligibility with a free consultation and a prescriber will take it from there.
The honest answer to which is better (tirzepatide or semaglutide) is that the trial data give tirzepatide a weight-loss edge at comparable doses, but the right choice for an individual depends on health history, lifestyle and clinical judgement. That is not a hedge; it is how medicine works. More on how the two treatments compare in practice is available if you want to read further before your consultation.
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