Wegovy vs Mounjaro: what's actually different between these two injections?

How do the two medicines actually work?

Wegovy contains semaglutide, a GLP-1 receptor agonist made by Novo Nordisk. It mimics a gut hormone that signals fullness to the brain, slows stomach emptying and reduces appetite. It acts on a single receptor pathway. You can read a clear plain-English overview on the NHS semaglutide medicines page.

Mounjaro contains tirzepatide, made by Eli Lilly, and is the only weight-loss medicine currently licensed in the UK that targets two receptors: GLP-1 and GIP. Both are gut hormones involved in appetite regulation and blood-sugar control. Activating both pathways simultaneously appears to produce a stronger appetite-suppressing effect than a single-receptor approach, which is reflected in the trial data.

Neither medicine is a quick fix. Both work best alongside reduced-calorie eating and increased physical activity, and both are prescription-only, meaning a prescriber must assess whether either is appropriate for you before treatment can start. Our weight-loss treatment overview explains how each fits into a broader approach.

What do the trial results actually show, and how should you read them?

A question our prescribers hear most weeks is some version of: "which one is stronger?" The trial evidence does lean one way, but the numbers deserve careful reading.

In the STEP 1 trial (68 weeks, adults without diabetes), semaglutide 2.4mg produced an average weight reduction of around 15%, compared with placebo, alongside lifestyle support. That was the data underpinning NICE's appraisal (NICE technology appraisal TA875) and the Wegovy licence.

In SURMOUNT-1 (72 weeks, similar population), tirzepatide at 15mg produced an average reduction of around 20 to 21%. The SURMOUNT-5 trial then put them head to head directly: in a 72-week open-label study of 751 adults with obesity and no diabetes, tirzepatide produced greater average weight loss than semaglutide 2.4mg, and if you want to understand how those results translate to a practical choice, our page on Monjaro vs Wegovy walks through what the evidence means for patients considering either option. This was reported in the New England Journal of Medicine in 2025 and informed the NICE committee's discussion in TA1026.

It is also worth noting that Wegovy now has a higher 7.2mg maintenance dose, approved by the MHRA in early 2026, with trial data showing around 20.7% average loss over 72 weeks, which narrows the gap with tirzepatide considerably. Results, though, are averages across trial populations; individual responses vary, and no trial result is a personal guarantee.

Trial figures are averages for study populations; individual results vary. Sources: NEJM STEP 1; NEJM SURMOUNT-1; NICE TA1026.

Who can be prescribed each one, and are there any clinical differences that matter?

The private licensed eligibility criteria are broadly similar for both. Adults with a BMI of 30 or above qualify, as do those with a BMI of 27 to 29.9 if they have at least one weight-related condition such as high blood pressure, type 2 diabetes, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds can apply for some ethnic backgrounds under UK clinical guidance. A prescriber assesses the full picture, not BMI alone.

There is one practical difference worth knowing if you take the oral contraceptive pill. For tirzepatide (Mounjaro), UK guidance recommends adding a non-oral method of contraception (such as condoms) for the first four weeks of treatment and for four weeks after each dose increase, because the pill's absorption may be reduced. There is no equivalent recommendation for semaglutide. If this applies to you, it is worth raising at consultation. The NHS England weight-management injections guidance sets this out clearly.

Side-effect profiles are similar for both: nausea, constipation, diarrhoea and indigestion are the most common, and tend to be most noticeable when starting or increasing the dose. A full safety overview is available via our frequently asked questions. Both medicines carry the MHRA Black Triangle, meaning any suspected side effects should be reported at yellowcard.mhra.gov.uk.

Does cost affect the choice between them?

Private treatment costs have changed significantly since Eli Lilly raised Mounjaro's UK list price from 1 September 2025. Market prices for both medicines vary by dose and provider; reported private-market figures for Mounjaro since that change range roughly £149 to £375 per month depending on dose. Wegovy pricing sits in a comparable range, and our page covering Manjaro vs Wegovy looks at how the costs and clinical profiles of the two medicines stack up side by side. Our Wegovy pricing page covers the cost picture for that medicine in more detail.

At nume, one price covers the consultation, prescription, treatment and 7-day aftercare, with free next-working-day delivery. We are not the cheapest option on the market, and that is a deliberate choice: what we offer is speed, clinical safety and a supply chain that runs through the licensed UK wholesale route. Current pricing is shown on the treatment page.

Price is a reasonable thing to consider. It should not be the deciding factor between two prescription medicines, though. The right medicine for you depends on your medical history, other medicines you take, your preferences around injection experience, and what a prescriber concludes after reviewing your full picture. You can read more about what that process involves on our about page, or explore a broader comparison of semaglutide products on our Wegovy vs Ozempic page, where the important distinction between a diabetes licence and a weight-management licence is covered.

Which of the two weight-loss injections suits you is a clinical judgement, not a ranking exercise, and if you are still weighing up the options our pages on what's the difference between Munjaro and Wegovy and on the Manjaro drug vs Wegovy cover the key distinctions in plain language. Speak to our prescribers and they will work through it with you.