Mounjaro vs Wegovy UK: Which Is Better for Weight Loss?
An in-depth comparison of Mounjaro and Wegovy — the two leading weight loss injections in the UK. Prices, results, side effects, and which is right for you.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) and Wegovy (semaglutide) both belong to the GLP-1 receptor agonist family, but they have a key pharmacological difference. Wegovy targets only the GLP-1 receptor, which reduces appetite, slows gastric emptying, and improves blood sugar control. Mounjaro targets both the GLP-1 and GIP receptors simultaneously — this dual mechanism is believed to produce a stronger appetite-suppressing effect and improved metabolic outcomes.
Both medications are administered as once-weekly subcutaneous injections using pre-filled pen devices. Both require a gradual dose escalation over several months to minimise side effects.
Weight Loss Results Compared
The weight loss data strongly favours Mounjaro. In the SURMOUNT clinical trials, Mounjaro at its highest dose (15mg) produced an average weight loss of approximately 22.5% of body weight over 72 weeks. In the STEP trials, Wegovy at its highest dose (2.4mg) produced approximately 14-17% body weight loss over a similar period.
To put this in real terms, a patient weighing 100kg could expect to lose approximately 22.5kg on Mounjaro versus 14-17kg on Wegovy. This represents a significant clinical difference that may influence your choice of medication, particularly if you have a large amount of weight to lose.
Price Comparison in the UK
Both Mounjaro and Wegovy are similarly priced in the UK private market. Mounjaro ranges from approximately £120 to £340 per month depending on dose and pharmacy. Wegovy ranges from approximately £150 to £300 per month. On an NHS prescription, both cost the standard £9.90 prescription charge in England, though eligibility criteria are strict for both.
When comparing value for money, Mounjaro arguably offers better cost-effectiveness given its superior weight loss efficacy. However, availability can fluctuate — Wegovy has experienced periodic supply shortages in the UK, while Mounjaro availability has been more consistent in 2026.
Side Effects Compared
Both medications share similar gastrointestinal side effects — nausea, diarrhoea, constipation, vomiting, and abdominal discomfort. Clinical trial data suggests the incidence of these side effects is broadly comparable between the two drugs, though some analyses suggest Mounjaro may have a slightly lower rate of nausea at equivalent efficacy levels.
Both carry rare risks of pancreatitis and gallbladder problems. Both are contraindicated in patients with a history of medullary thyroid carcinoma or MEN2 syndrome. Overall, the side effect profiles are sufficiently similar that this is unlikely to be the deciding factor for most patients.
Availability and Eligibility in the UK
Both Mounjaro and Wegovy are available on the NHS in England, but eligibility is extremely restricted to patients with a BMI of 40+ (or 37.5+ for certain ethnic backgrounds) with multiple comorbidities. Wait times can be up to 18 months in some regions.
Privately, both are accessible through online pharmacies with broader eligibility — typically BMI 30+ or BMI 27+ with a weight-related condition. Both require a clinical consultation and prescription from a qualified prescriber. Mounjaro is available from a wider range of UK pharmacies, and comparing prices across providers can save you significant amounts each month.
Which Should You Choose?
For most patients, Mounjaro is the stronger choice based on clinical efficacy data — it produces significantly greater weight loss than Wegovy at comparable price points. If maximum weight loss is your primary goal, Mounjaro's dual GIP/GLP-1 mechanism offers a clear advantage.
However, Wegovy may be preferable if you have already had success with semaglutide-based medications (such as Ozempic for diabetes), if Mounjaro is unavailable from your preferred pharmacy, or if your prescriber recommends it based on your specific medical history. Both are excellent medications, and the best choice depends on your individual circumstances, response, and prescriber advice.
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