If you're considering a prescription injectable for weight management in the UK, you've likely come across both Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4 mg). Both are approved for weight loss, but they differ in important ways.
What's the Same?
Before diving into the differences, it's worth noting the similarities:
- Both are once-weekly injections administered with a pre-filled pen
- Both require a gradual dose escalation to minimise side effects
- Both are indicated for adults with obesity (BMI ≥ 30) or overweight (BMI ≥ 27) with a weight-related comorbidity
- Both should be used alongside a reduced-calorie diet and increased physical activity
How They Differ
The fundamental difference is in their mechanism:
- Wegovy is a GLP-1 receptor agonist only
- Mounjaro is a dual GLP-1 and GIP receptor agonist
This dual action means tirzepatide engages an additional hormonal pathway, which clinical data suggests translates to greater weight loss on average.
Weight Loss Results
Clinical trials have shown meaningful differences:
- Wegovy (STEP 1 trial): participants lost an average of approximately 14.9% of body weight over 68 weeks
- Mounjaro (SURMOUNT-1 trial): participants on the 15 mg dose lost an average of approximately 22.5% of body weight over 72 weeks
These are average figures — individual results can vary considerably based on adherence, diet, and activity levels.
Side Effects
Both medications share similar gastrointestinal side effects, including nausea, vomiting, diarrhoea, and constipation. These are generally most noticeable during the dose escalation phase and tend to improve over time. There is no strong evidence that one is significantly better tolerated than the other, though some patients may find they respond differently to each.
Availability and Cost in the UK
Wegovy received NICE approval for weight management on the NHS in certain cases, though access has been limited by supply constraints. Mounjaro is also available and gaining wider access through both NHS and private prescriptions.
Private prescription costs vary:
- Wegovy: approximately £150–£300 per month depending on dose and pharmacy
- Mounjaro: approximately £150–£250 per month depending on dose and pharmacy
Use MedsLens to compare current prices across registered UK pharmacies and find the best deal.
Making Your Decision
Both are excellent options for medically supervised weight management. Your prescriber will consider your medical history, other medications, and treatment goals when recommending one over the other. If cost or availability is a factor, comparing pharmacy prices is essential.