Choosing between Mounjaro and Wegovy can feel overwhelming. Both are MHRA-approved injectable weight loss treatments available in the UK, but they have important differences in how they work, their effectiveness, and their side effect profiles. This comprehensive comparison will help you understand which option might be better suited to your needs.
Active Ingredients and Mechanism of Action
The fundamental difference between these two medications lies in their active ingredients and how they interact with your body.
Wegovy contains semaglutide, a GLP-1 receptor agonist that mimics the natural hormone GLP-1, which your body releases after eating. It works by:
- Telling your brain that you’re full
- Slowing down how quickly food leaves your stomach
- Regulating appetite and reducing calorie intake
Mounjaro contains tirzepatide and works differently – it targets two hormone pathways: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). This dual action gives it a broader effect on appetite regulation, blood sugar control, and energy storage.
| Feature | Wegovy | Mounjaro |
| Active Ingredient | Semaglutide | Tirzepatide |
| Receptor Targets | GLP-1 only | GLP-1 and GIP |
| Manufacturer | Novo Nordisk | Eli Lilly |
| Dose Range | 0.25mg – 2.4mg (7.2mg now approved) | 2.5mg – 15mg |
Weight Loss Results Compared
Clinical trials have shown that Mounjaro generally produces greater average weight loss than Wegovy at standard doses. A 2025 study found that over 72 weeks, participants lost an average of 21.6% of their body weight on Mounjaro (15mg) compared to 15.4% on Wegovy (2.4mg).
However, the introduction of the higher-strength Wegovy 7.2mg dose has narrowed this gap significantly. This new dose, approved by the MHRA in January 2026, has shown average weight loss of 19-21% of baseline body weight over 72 weeks. Approximately one third of participants achieved weight loss of 25% or more.
Side Effects and Tolerability
Both medications can cause gastrointestinal side effects in 77-79% of patients. However, there are some differences:
- Wegovy tends to have higher vomiting rates (21% vs 15% for Mounjaro)
- Mounjaro may cause more nausea at its highest doses
- Treatment discontinuation due to side effects was 8% for Wegovy vs 6% for Mounjaro, suggesting Mounjaro may be slightly better tolerated overall
Most side effects are mild to moderate and improve as your body adjusts to the medication.
Dosing and Administration
Both medications are self-administered via a prefilled injection pen once weekly. They follow a dose escalation approach starting low and gradually increasing over several weeks to minimise side effects.
Wegovy has five dose levels (0.25mg, 0.5mg, 1.0mg, 1.7mg, 2.4mg), with the new 7.2mg dose now available. Mounjaro has six dose levels (2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, 15mg). Patients typically move up a dose each month until reaching their maintenance dose.
Can You Switch Between Them?
Switching from one medication to the other is possible under medical supervision, but you may need to drop back down to the initial starting dose. You’ll need to complete a new online consultation before changing treatments.
To learn more about weight loss injections and which option might be right for you, visit YourPharmacy for expert guidance and personalised support.
