Mounjaro and Wegovy are the two most effective GLP-1 weight loss medications available in the UK. Both are once-weekly injections, both require a prescription following a clinical consultation, and both produce substantial weight loss. The question of which is better for you is more nuanced than the headline trial numbers suggest — and the answer changed meaningfully in early 2026 with the approval of Wegovy 7.2mg.
How they work differently
Wegovy (semaglutide) is a GLP-1 receptor agonist. It mimics the GLP-1 hormone released after eating, telling the brain you are full, slowing gastric emptying, and reducing appetite. Mounjaro (tirzepatide) does the same — but also activates a second receptor: GIP (glucose-dependent insulinotropic polypeptide). GIP appears to work synergistically with GLP-1, amplifying the appetite-suppressing effect and producing broader metabolic changes. This dual mechanism is why Mounjaro tends to produce greater average weight loss.
What the clinical trials show
The SURMOUNT-5 trial, published in the New England Journal of Medicine in May 2025, was the first head-to-head comparison of the two drugs at clinically relevant doses. Results favoured tirzepatide clearly: participants on Mounjaro lost an average of 20.2% of body weight compared to 13.7% for those on semaglutide (Wegovy at its then-maximum 2.4mg dose) over 72 weeks.
Side effects were broadly similar between the two. Around 77–79% of participants in both groups reported at least one side effect — mostly gastrointestinal. Fewer participants discontinued Mounjaro due to side effects (around 6%) than Wegovy (around 8%).
Then in January 2026, the MHRA approved Wegovy 7.2mg — a new dose three times higher than the previous maximum. The STEP UP trial showed this dose achieving 20.7% average weight loss over 72 weeks, with one in three patients losing 25% or more. This essentially matches Mounjaro's headline figure, narrowing the gap significantly.
| Drug | Trial | Avg. weight loss | Duration |
|---|---|---|---|
| Mounjaro 15mg | SURMOUNT-1 | ~22.5% | 72 weeks |
| Mounjaro vs Wegovy (head-to-head) | SURMOUNT-5 | 20.2% vs 13.7% | 72 weeks |
| Wegovy 2.4mg | STEP-1 | ~14.9% | 68 weeks |
| Wegovy 7.2mg | STEP UP | 20.7% | 72 weeks |
The cardiovascular picture
Wegovy has a significant advantage here. The SELECT trial demonstrated that semaglutide reduces the risk of major cardiovascular events — heart attack, stroke or cardiovascular death — by around 20% in people with established cardiovascular disease. This formed the basis of the new NICE approval in April 2026 for Wegovy as a cardiovascular risk-reduction medicine, a separate indication from weight management entirely.
Mounjaro does not currently have this NICE approval for cardiovascular indication in the UK, though early data from the SURPASS-CVOT trial is promising. For most people taking these drugs purely for weight loss this distinction may not be clinically decisive, but for anyone with existing cardiovascular disease it is worth discussing explicitly with a prescriber.
Cost and NHS access
Following Eli Lilly's September 2025 UK price rise, Mounjaro is now considerably more expensive at higher doses for private patients. The 15mg dose rose from £122 to £330 per month. Wegovy is now generally the more affordable option at equivalent dose levels. On the NHS, both are available for eligible patients — Mounjaro through primary care and specialist services following NICE TA1026, and Wegovy through specialist services under NICE TA875 and via GPs for cardiovascular risk reduction following the April 2026 guidance.
So which should you choose?
There is no universal answer, but some considerations are reasonably clear. If efficacy is the primary criterion and cost is not a constraint, Mounjaro has shown greater average weight loss across most head-to-head data. If cardiovascular protection is relevant to your health history, Wegovy has the stronger evidence base and the NICE approval to support it. If cost is the primary consideration, Wegovy is now materially cheaper at higher doses. And if you have previously tolerated semaglutide well — for example, through Ozempic for diabetes — Wegovy may be the natural choice for continuing in the same drug class.
The most important factor is engaging with a prescriber who can make a recommendation based on your individual circumstances.
- BHF: Mounjaro vs Wegovy — behind the headlines (2025)
- SURMOUNT-1 trial, NEJM (2022)
- SURMOUNT-5 head-to-head trial, NEJM (May 2025)
- STEP UP trial — Wharton et al., The Lancet (November 2025)
- NICE TA1026: tirzepatide for obesity
- NICE TA875: semaglutide for obesity