Mounjaro or Wegovy: which is better for weight loss?

What the evidence shows: trial results and the 2025 head-to-head

Mounjaro and Wegovy are the two leading weight-management injections licensed in the UK, and the question of which performs better is one our prescribers are asked most weeks. For a long time, comparisons relied on separate trial programmes. SURMOUNT-1 reported around 20–21% average body-weight reduction over 72 weeks at Mounjaro's highest dose, while the STEP 1 trial, published in the New England Journal of Medicine, showed roughly 15% average reduction over 68 weeks with Wegovy 2.4mg, meaningful results in both cases, but not a clean comparison.

Then came SURMOUNT-5, published in the New England Journal of Medicine in 2025: a direct head-to-head trial in 751 adults with obesity and no diabetes, run over 72 weeks, which found tirzepatide produced greater average weight loss than semaglutide 2.4mg. That evidence is now reflected in NICE's appraisal of tirzepatide (TA1026), which notes that indirect comparisons favour tirzepatide. It is also worth knowing that a higher Wegovy dose (7.2mg, approved by the MHRA in early 2026) narrows that gap considerably, with trials reporting around 20.7% average loss over 72 weeks. So the picture continues to develop, and if you want a closer look at how these two stack up, our Wegovy or Mounjaro comparison walks through the evidence in more detail.

Numbers from trials are averages across large groups. Individual responses vary considerably, and both medicines show a wide range of outcomes in practice.

How the two medicines work, and why that matters for some people

Mounjaro activates two gut-hormone receptors: GIP and GLP-1. Wegovy activates one: GLP-1. That dual action is the most commonly cited reason for tirzepatide's stronger average results, but the mechanism difference also has practical implications for how each medicine sits alongside other treatments you may already be taking.

The contraception difference is worth flagging specifically. Women using oral contraceptives who start Mounjaro are advised to use an additional non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because slowed gastric emptying can reduce pill absorption. Semaglutide does not carry the same evidence-based advisory. This is covered in detail on the safety comparison page, and the NHS England guidance on weight-management injections addresses it directly.

Eligibility, NHS access and what private treatment covers

Both medicines share similar private eligibility: adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, high cholesterol or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. BMI alone does not decide suitability, a prescriber looks at the whole picture, including other medicines and medical history.

On the NHS, access to either medicine is phased and limited. NICE's recommendation for tirzepatide (TA1026) is being rolled out gradually by BMI and number of qualifying conditions; Wegovy's NICE recommendation (TA875) is restricted to specialist weight management services and carries a two-year maximum. Waiting lists are often long for both. A private route through a regulated online pharmacy removes that wait, subject to clinical suitability, you can read more about what that process involves on our treatment page.

If you are weighing up cost as part of this decision, the UK price comparison covers what private treatment typically costs for each, and what that price should include. Treatment pricing at nume follows a single transparent structure with no subscription and no auto-renewal.

Which suits you is a clinical decision, not a headline result

If you are deciding between Mounjaro and Wegovy, you are probably already past the stage of wondering whether these medicines work. The harder question is which one fits your situation, your health history, any medicines you are already taking, your preferences around injection devices and, for some people, whether needles are a factor at all. Oral semaglutide (the Wegovy tablet, approved by the MHRA in June 2026) is now a licensed option for those who would rather avoid injections entirely; you can explore that on our weight-loss treatment overview.

It is genuinely understandable to feel a little overwhelmed at this point. There is a lot of information online (some of it good, some of it not) and these are prescription medicines that require a proper clinical assessment before anyone should be taking them. The comparison that matters most is the one your prescriber makes with your specific details in front of them. Our clinical team makes that assessment individually for every patient, the same day you submit your consultation. No algorithm, no shortcut.

Curious about how tirzepatide compares to Ozempic specifically? The Mounjaro vs Ozempic page covers that, including the important licensing distinction, Ozempic is not authorised for weight loss in the UK. You might also find it useful to read about which is better, Ozempic or Mounjaro, including how the two medicines differ in dose, mechanism and licensed use, or, if you are considering an oral option alongside an injection, our page on Rybelsus vs Mounjaro compares the tablet form of semaglutide directly with tirzepatide.