Mounjaro®
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Start journey Learn moreHow tirzepatide and semaglutide compare: mechanism, evidence and what actually differs
You've heard both names, here's what's actually going on
The confusion is understandable. Both medicines appear in the same conversations, both involve weekly injections, both are used for weight management, and some online sellers present them almost interchangeably. Patients transferring from one clinic to another often find the two names used in ways that blur rather than clarify the difference.
Semaglutide is the active ingredient in Wegovy (the injection licensed in the UK for weight loss) and in Ozempic, though Ozempic is licensed solely for type 2 diabetes and is not a weight-loss medicine in UK law, a distinction the NHS medicines page for semaglutide sets out clearly. If you've seen Ozempic discussed for weight loss, that's a different context. Tirzepatide is the active ingredient in Mounjaro, and if you're wondering whether tirzepatide is the same as Ozempic, they are entirely separate medicines with different active ingredients and different licensed uses.
The pharmacological difference matters more than a brand name. Semaglutide is a GLP-1 receptor agonist, it mimics a gut hormone called glucagon-like peptide-1, which slows digestion, reduces appetite and lowers blood sugar. Tirzepatide is a dual GIP and GLP-1 receptor agonist, the only medicine of its kind licensed in the UK for weight management. It activates both GLP-1 and the glucose-dependent insulinotropic polypeptide (GIP) pathway. Whether that dual action translates into meaningful differences for individuals is something our prescribers explore at consultation.
What the head-to-head trial actually showed
For years, comparing tirzepatide and semaglutide meant looking at separate trials with different populations, imprecise at best. That changed with SURMOUNT-5, an open-label randomised trial published in the New England Journal of Medicine in 2025, which put tirzepatide directly against semaglutide 2.4mg in 751 adults with obesity and no diabetes, over 72 weeks. Tirzepatide produced greater average weight reduction. The NICE appraisal of tirzepatide (TA1026) also noted indirect comparisons favouring tirzepatide, though NICE guidance acknowledges the limits of cross-trial analysis.
The earlier individual trials are still worth understanding. In SURMOUNT-1 (tirzepatide, 72 weeks), participants at the 15mg dose achieved around 20–21% average body-weight reduction. In STEP 1 (semaglutide 2.4mg, 68 weeks), the average reduction was around 15%. A newer, higher-dose semaglutide pen (the 7.2mg Wegovy, approved by the MHRA in April 2026) narrows that gap, with trials reporting around 20.7% average weight loss over 72 weeks. So the picture is shifting, and if you want to dig into which suits you better, semaglutide or tirzepatide, the right dose and population matter enormously. The question of whether semaglutide matches tirzepatide looks different depending on which dose and which population you consider.
None of this means one medicine is objectively better. Trial averages describe groups; prescribers think about individuals. Side-effect tolerance, injection-site preference, existing health conditions and other medicines all shape which treatment makes sense for a specific person.
Comparing tirzepatide and semaglutide side by side
| Feature | Tirzepatide (Mounjaro) | Semaglutide (Wegovy injection) |
|---|---|---|
| Drug class | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist |
| UK brand name (weight loss) | Mounjaro | Wegovy |
| Manufacturer | Eli Lilly | Novo Nordisk |
| Starting dose | 2.5mg weekly | 0.25mg weekly |
| Maximum licensed dose | 15mg weekly | 7.2mg weekly (from April 2026) |
| Average weight loss in trials (highest dose, 68–72 weeks) | ~20–21% (SURMOUNT-1, NEJM) | ~15% at 2.4mg (STEP 1); ~20.7% at 7.2mg |
| Head-to-head result (SURMOUNT-5, NEJM 2025) | Greater average reduction | Comparator arm |
| UK licence for weight loss | Yes (BMI ≥30, or ≥27 with comorbidity) | Yes (BMI ≥30, or ≥27 with comorbidity) |
For a more detailed look at the two UK brands, the Wegovy vs Mounjaro comparison covers practical questions including side effects and titration.
What this means when you're choosing between them
Say it's a Monday morning, maybe you've just been paid and you've decided today is the day to look into this properly. You've seen both names everywhere and people sometimes ask whether tirzepatide is the same as Wegovy, which is a fair question given how often the two come up together. They are genuinely different, and the choice between them is a clinical one.
Both medicines share a similar side-effect profile: nausea, constipation, indigestion and occasional fatigue are the most common, usually most noticeable in the early weeks of treatment or after a dose increase. The NHS tirzepatide page sets out the full picture for Mounjaro, including when to seek urgent help. If you're also taking an oral contraceptive, there's an additional practical point for tirzepatide specifically: MHRA guidance recommends adding a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because the pill's absorption may be reduced. Those asking whether semaglutide is the same as Mounjaro will find that interaction is one of several practical differences between the two, since it has not been demonstrated for semaglutide.
The prescriber's job (and ours at nume's clinical team) is to weigh all of that against your health history, your current medicines and your goals. Our weight-loss treatments overview explains how the two fit into a broader clinical assessment. For a direct conversation, speak to our prescribers through a free consultation and let a real clinician match the evidence to your situation.
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