Mounjaro®
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Start journey Learn moreMounjaro and Wegovy side by side: mechanism, evidence, and what to consider
The decision most people are actually making
When someone searches "is Wegovy tirzepatide", they're usually not after a chemistry lesson. They've heard about two injections that help with weight loss, they know one might work better than the other, and they want to understand what they'd actually be choosing between. That's a reasonable place to start.
Mounjaro (tirzepatide) activates two gut-hormone receptors, GIP and GLP-1, which together reduce appetite and slow gastric emptying. Wegovy (semaglutide) activates one, the GLP-1 receptor. Both slow how quickly your stomach empties and reduce the urge to eat; the dual-receptor action in tirzepatide is what makes it mechanistically distinct. You can read more about how tirzepatide and semaglutide differ at a molecular level if that level of detail is useful.
There's a common misconception that Wegovy and Ozempic are interchangeable for weight loss. They both contain semaglutide, but Ozempic is licensed for type 2 diabetes, not weight management. The distinction between Ozempic, Wegovy and tirzepatide catches a lot of people out, and it's worth being clear on before you have any clinical conversation.
What the trial evidence actually shows
Both medicines have strong clinical trial data behind them. In the STEP 1 trial (68 weeks, semaglutide 2.4mg), participants lost an average of around 15% of their body weight, as published in the New England Journal of Medicine. SURMOUNT-1 tested tirzepatide over 72 weeks and found average weight reduction of around 20–21% at the 15mg dose.
A more direct comparison came from the SURMOUNT-5 trial, a head-to-head study in 751 adults with obesity and no diabetes, run over 72 weeks. Tirzepatide produced greater average weight loss than semaglutide 2.4mg. NICE's appraisal of tirzepatide (TA1026) noted that indirect comparisons also favour tirzepatide, and the SURMOUNT-5 result gave that picture a direct-evidence foundation. Wegovy's newer 7.2mg dose narrows the gap somewhat; trial data reported around 20.7% average loss at that higher dose, which approaches tirzepatide's top-dose results.
Those numbers all come from specific trial populations. Real-world results vary. Neither medicine is a guarantee of any particular outcome for any individual.
| Feature | Mounjaro (tirzepatide) | Wegovy (semaglutide injection) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| Manufacturer | Eli Lilly | Novo Nordisk |
| UK licence (weight) | BMI ≥30, or ≥27 with a weight-related condition | BMI ≥30, or ≥27 with a weight-related condition |
| Average trial weight loss (maintenance dose) | ~20–21% at 15mg (SURMOUNT-1, NEJM) | ~15% at 2.4mg (STEP 1, NEJM); ~20.7% at 7.2mg |
| Administration | Once-weekly subcutaneous injection | Once-weekly subcutaneous injection |
| Starting dose | 2.5mg (tolerability phase) | 0.25mg (tolerability phase) |
Eligibility, side effects, and cost: the practical factors
The licensed eligibility criteria are similar for both. Adults with a BMI of 30 or above qualify, as do those with a BMI of 27 or above alongside a weight-related health condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Lower thresholds apply for some ethnic backgrounds under UK guidance. BMI alone doesn't determine approval; a prescriber looks at the whole clinical picture. An overview of weight-loss treatment options covers this in more detail.
Both medicines share a broadly similar side-effect profile, led by gastrointestinal symptoms: nausea, loose stools, constipation, indigestion and occasional vomiting. These tend to be most noticeable after starting treatment or after each dose increase, and they often settle as the body adjusts. The NHS medicines page for tirzepatide and its equivalent for semaglutide both carry detailed, patient-level side-effect information.
On cost, Eli Lilly raised Mounjaro's UK list price significantly from September 2025; private prices for both medicines now typically sit in the £149–£375 per month range depending on dose and provider, as widely reported. A direct price comparison between Mounjaro and Wegovy sets out the full cost picture. Neither medicine is cheap, and the right one for you isn't necessarily the cheaper one.
Which medicine suits you is a clinical conversation
Picking between two prescription medicines based on a web comparison is the start of the process, not the end of it. Your medical history, any current medications, how you feel about injections, your body weight and your health goals all feed into a prescriber's thinking. A named clinician, not software, reads every consultation at nume before any decision is made. If you're still working out whether tirzepatide and Wegovy are really the same thing, that page unpicks the question directly before you go further. A fuller Wegovy versus Mounjaro breakdown explores the clinical differences further, and the semaglutide-or-tirzepatide question is answered from a slightly different angle if that framing is more useful.
Which suits you is a clinical decision our prescribers make with you. If you'd like that conversation, start your free consultation and a GPhC-registered prescriber will review your answers the same day.
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