Mounjaro vs Wegovy: Comparing Two Prescription Weight-Loss Injections

Step 1, Understand what each medicine actually does

Mounjaro (tirzepatide, made by Eli Lilly) activates two gut-hormone receptors: GIP and GLP-1. Both are involved in appetite signalling and blood-sugar regulation. No other weight-loss medicine licensed in the UK targets both pathways simultaneously. Wegovy (semaglutide, made by Novo Nordisk) activates GLP-1 alone. Both slow gastric emptying and reduce appetite; Mounjaro's dual action is the main pharmacological difference between them.

It matters because the receptor combination appears to produce stronger average weight loss at the highest doses, though individual responses vary considerably. Worth knowing before you compare any headline figures: the trials used different populations, different follow-up periods, and different definitions of "maintenance dose", so like-for-like comparisons need careful handling. A question our prescribers hear most weeks is whether one is simply "better", the honest answer is that it depends on the person in front of them.

Neither medicine is appropriate for under-18s, and neither is recommended during pregnancy, while breastfeeding, or when trying to conceive. Those points apply equally to both.

Step 2, Look at what the trial evidence actually shows

In SURMOUNT-1, Mounjaro produced an average body-weight reduction of around 20–21% over 72 weeks at the 15mg maintenance dose; some analyses put the figure slightly higher. SURMOUNT-1 involved 2,539 adults with obesity. The STEP 1 trial, published in the New England Journal of Medicine, reported approximately 15% average weight loss for Wegovy 2.4mg over 68 weeks.

A direct head-to-head comparison now exists. The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, randomised 751 adults with obesity and no diabetes, and found that tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks. NICE's appraisal of tirzepatide (TA1026) references this and notes that indirect comparisons also favour tirzepatide, while acknowledging the evidence base continues to develop.

One important nuance: Wegovy's 7.2mg dose, approved by the MHRA in January 2026 and available as a dedicated single-dose pen from April 2026, reported around 20.7% average weight loss over 72 weeks in its supporting trial, narrowing the gap with tirzepatide at the highest doses. The 7.2mg pen carries a BMI threshold of 30 or above; it is not available for the cardiovascular indication.

Figures in the table are from published trial data and NICE appraisals; individual results vary.

Step 3, Check the eligibility picture for each

Both medicines share a common licensed starting point for private prescribing: adults with a BMI of 30 or above, or 27 to 29.9 alongside at least one weight-related condition such as high blood pressure, type 2 diabetes, high cholesterol, or obstructive sleep apnoea. Lower thresholds apply for some ethnic backgrounds under UK clinical guidance. BMI alone never settles the question; a prescriber weighs your full medical history, current medications, and any contraindications before prescribing either.

On the NHS the picture differs between the two. NICE's recommendation for Wegovy (TA875) restricts it to a maximum of two years within a specialist weight management service. Mounjaro's NHS rollout is phased by cohort, NHS England's weight-management guidance sets out the current qualifying BMI and comorbidity thresholds, which are tightening gradually through 2026 and 2027. Many people find the NHS criteria are strict or waiting lists long, which is why private routes through a regulated pharmacy exist.

If you've already started one medicine and are wondering about switching, switching between Mounjaro and Wegovy is something our prescribers assess on a case-by-case basis, it is not a straightforward swap and requires clinical review.

Step 4, Weigh the practical differences, including cost

Day-to-day use is similar: both are once-weekly subcutaneous injections into the abdomen, thigh, or upper arm, kept refrigerated. Neither requires special equipment beyond rotating the site and using a fresh needle each time. If you are still weighing up which of the two options fits your situation, our page on how Wegovy and Mounjaro compare sets out the key differences in one place. Both carry a GI-led list (nausea, loose stools, constipation, reflux) typically most pronounced after starting or moving up a dose, then settling. The tirzepatide-specific contraception note is worth knowing: women taking oral contraceptives should use an additional non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because Mounjaro may reduce oral contraceptive absorption. No equivalent warning exists for semaglutide.

On cost, prices for both medicines have shifted since Eli Lilly raised Mounjaro's UK list price in September 2025, with typical private monthly costs now ranging roughly £149–£375 depending on dose and provider. A full price breakdown including what's included and what's often left out is on our Mounjaro vs Wegovy price comparison page. The short version: any legitimate price for a prescription medicine should include clinical assessment, not just the pen.

One quick check worth doing: any online pharmacy you consider should appear on the GPhC register. Takes under a minute. If the seller isn't listed, that's a hard stop, the MHRA has warned repeatedly about counterfeit weight-loss pens circulating online, some containing dangerous substitutes.

For a deeper look at how the two options compare from a different angle, the pages on which might suit you better and whether one is clinically superior cover the nuance our prescribers consider. And if Ozempic has come up in your research, our Mounjaro vs Ozempic comparison explains why Ozempic's licence matters: it is approved for type 2 diabetes, not weight management, and should not be conflated with either of these options.

Which medicine suits you is a clinical decision our prescribers make with you.