Mounjaro®
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Start journey Learn moreWhat the trial evidence and licensing actually tell you about these two medicines
The decision you're probably trying to make
You've likely been reading about both medicines for a while. Maybe you've seen the head-to-head trial results and wondered whether tirzepatide is simply the better drug, full stop. Maybe a GP mentioned semaglutide and you're not sure if there's something newer worth asking about. That feeling of wanting certainty before committing is completely reasonable, these are prescription medicines with real effects, not supplements you can trial and discard.
The practical comparison comes down to four things: how each medicine works, what the evidence says about results, which one your health profile suits, and what's realistic given your circumstances. Those first two questions can be answered here. The last two need a prescriber.
One clarification before going further: Ozempic is also semaglutide, but it is licensed for type 2 diabetes, not weight loss. If weight management is your goal, the licensed semaglutide options in the UK are Wegovy (injection) and the recently approved Wegovy tablet. Comparing semaglutide or tirzepatide for weight loss means comparing those products, not Ozempic. You can read more on that distinction between Ozempic, tirzepatide and semaglutide separately.
How the mechanisms differ, and why it matters
Semaglutide is a GLP-1 receptor agonist. It mimics a gut hormone that signals fullness, slows how quickly food leaves your stomach, and reduces appetite. It works on one receptor pathway. That single pathway has been enough to produce consistent, significant weight loss in large clinical trials.
Tirzepatide acts on two receptor pathways simultaneously: GLP-1 and GIP. GIP is a second gut hormone involved in appetite regulation and metabolic function. Activating both pathways together appears to produce a stronger appetite-reduction effect than either alone, which is the main reason the trial results for tirzepatide tend to be higher. It is the only dual-agonist weight-loss medicine currently licensed in the UK, sold as Mounjaro. If you want the full breakdown of how Mounjaro and Wegovy compare on a practical level, our Wegovy versus Mounjaro page covers that in detail.
The NHS medicines page for tirzepatide and the equivalent page for semaglutide explain both mechanisms in patient-level language if you want to read further.
What the head-to-head evidence actually shows
The clearest way to compare the two medicines is the SURMOUNT-5 trial, a 72-week open-label study published in the New England Journal of Medicine in 2025. It directly compared tirzepatide against semaglutide 2.4mg in adults with obesity and no diabetes. Tirzepatide produced a meaningfully greater average reduction in body weight. That is the strongest evidence available and it favours tirzepatide, which is reflected in NICE's appraisal of tirzepatide (TA1026).
The comparison table below summarises the key figures:
| Factor | Semaglutide (Wegovy injection, 2.4mg) | Tirzepatide (Mounjaro, 15mg) |
|---|---|---|
| Average weight loss in trials | ~15% at 68 weeks (STEP 1, NEJM 2021) | ~20–21% at 72 weeks (SURMOUNT-1, NEJM 2022) |
| Head-to-head comparison | Lower average loss vs tirzepatide (SURMOUNT-5, NEJM 2025) | Greater average loss vs semaglutide 2.4mg (SURMOUNT-5, NEJM 2025) |
| Receptor pathway(s) | GLP-1 only | GLP-1 + GIP (dual agonist) |
| UK injection dosing start | 0.25mg, titrated to 2.4mg (or 7.2mg) | 2.5mg, titrated to up to 15mg |
| Oral option licensed in UK? | Yes, Wegovy tablet (25mg maintenance, approved June 2026) | No |
| NICE-recommended on NHS? | TA875 (via specialist weight management services, max 2 years | TA1026) phased NHS rollout; widely available privately |
The 7.2mg Wegovy pen, approved by the MHRA in April 2026, does close some of the gap, trials at that higher dose reported around 20.7% average loss over 72 weeks. It is worth knowing that exists. Our detailed side-by-side of Wegovy and Mounjaro covers those updated figures.
Which one is the right fit for you?
Raw trial averages do not determine individual outcomes. Both medicines produce a wide range of results depending on how someone's body responds, their starting weight, their diet, their activity level, and how well they tolerate the titration schedule. Some people lose substantially more than the trial average; others less. There is no reliable way to predict which category any individual falls into before treatment begins.
Prescribers weigh other factors too: whether you have type 2 diabetes (both medicines are licensed for that), whether you prefer an injection or would rather try a tablet, how your medical history looks alongside the contraindications, and whether you have had any previous GLP-1 treatment that provides a clue about your likely response. If you want a prescriber's perspective on the mounjaro-vs-semaglutide question specifically, our Mounjaro or semaglutide comparison page and the related semaglutide or tirzepatide overview both go into the clinical nuances, and if you are still weighing up which of the two medicines is better suited to your situation, that page works through the question in more depth.
Both medicines are prescription-only and require a full clinical assessment before any prescription is written. That assessment is what converts a population-level trial result into a recommendation that is actually right for you. Our clinical team reviews every consultation personally. If you are ready to find out which medicine your health picture supports, start your free consultation and a prescriber will work through it with you.
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