Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4mg) are currently the two most effective prescription weight loss treatments available in the UK. Both are weekly injectable GLP-1 receptor agonists, but they work slightly differently and produce different average results. Choosing between them depends on your individual health profile, budget, and treatment goals.
Wegovy contains semaglutide, which mimics the GLP-1 hormone to reduce appetite and slow gastric emptying. Mounjaro contains tirzepatide, which mimics both GLP-1 and GIP hormones — this dual action is believed to explain why Mounjaro typically produces greater weight loss than Wegovy in clinical trials.
| Metric | Mounjaro (SURMOUNT-1) | Wegovy (STEP-1) |
|---|---|---|
| Average weight loss | ~22.5% body weight | ~14.9% body weight |
| Patients losing >20% weight | 57% | 32% |
| Patients losing >15% weight | 63% | 37% |
| Trial duration | 72 weeks | 68 weeks |
| Highest dose tested | 15mg weekly | 2.4mg weekly |
Clinical trial results are averages. Individual results vary significantly based on diet, exercise, starting weight, and other factors. These results were achieved alongside a reduced-calorie diet and increased physical activity.
Both treatments share a similar side effect profile, as they work on the same GLP-1 pathway. The most common side effects for both are gastrointestinal: nausea, vomiting, diarrhoea, and constipation. These are typically worst during dose increases and improve over time. Mounjaro's additional GIP action does not appear to significantly increase the risk of side effects compared to Wegovy.
| Treatment | Starting Dose | Cheapest Monthly Price | Discount Codes Available |
|---|---|---|---|
| Mounjaro (tirzepatide) | 2.5mg | From ~£139/month | Yes — 40+ pharmacies |
| Wegovy (semaglutide) | 0.25mg | From ~£159/month | Yes — 20+ pharmacies |
If maximising weight loss is your primary goal and you have no contraindications to either treatment, Mounjaro's clinical trial data suggests it is the more effective option. However, Wegovy has a longer track record in the UK market, more long-term safety data, and may be preferred by patients who have already been using semaglutide (e.g. Ozempic) and want to continue with the same active ingredient at the higher weight-loss dose.