Wegovy vs Mounjaro: What Are the Real Benefits of Each?

Do they work in the same way, or is there a meaningful difference in mechanism?

Wegovy (semaglutide) activates a single gut-hormone receptor (GLP-1) which slows gastric emptying and reduces appetite. Mounjaro (tirzepatide) activates two: GLP-1 and GIP. That dual action is not a marketing refinement; it produces a distinct physiological profile. GIP receptors are expressed in fat tissue and the brain in ways that GLP-1 receptors are not, which is thought to contribute to the additional weight loss seen with tirzepatide in clinical trials. Mounjaro is, at the moment, the only dual-agonist weight-loss medicine licensed in the UK. You can read more about the mechanism behind each in our full Wegovy vs Mounjaro overview.

Both medicines are once-weekly subcutaneous injections. Both are titrated gradually (starting low and stepping up over several months) to give your system time to adjust. Neither is taken as a fixed maintenance dose from day one. The NHS medicines page for tirzepatide and for semaglutide are the clearest patient-level summaries of how each works, and they are worth bookmarking alongside your Patient Information Leaflet.

What do the clinical trials say about weight-loss results?

The headline figures come from two large phase-3 trials and, crucially, one direct head-to-head comparison. SURMOUNT-1 (tirzepatide, 72 weeks, 2,539 participants) recorded average body-weight reductions of around 20–21% at the highest dose, among the strongest results ever seen in a weight-management medicine. STEP 1 (semaglutide 2.4mg, 68 weeks) showed around 15% average reduction, itself a landmark at the time. The SURMOUNT-1 paper in the New England Journal of Medicine is the primary source for the tirzepatide figures.

SURMOUNT-5 (published 2025) put the two medicines head-to-head for the first time in a randomised trial of 751 adults with obesity and no diabetes, over 72 weeks. Tirzepatide produced greater average weight loss than semaglutide 2.4mg, and if you want a thorough breakdown of how the two compare across doses and populations, our detailed look at whether Wegovy or Mounjaro is better walks through the evidence. The NICE appraisal of tirzepatide (TA1026) references the indirect and direct comparative evidence in its committee discussion. No trial has definitively tested tirzepatide against Wegovy 7.2mg; that comparison remains open.

One practical check worth making before you assume a dose: pull up the actual trial arms each figure comes from. A 20% headline is sometimes the highest dose, at 72 weeks, in the per-protocol population, not the average across all participants at six months. Context changes the number significantly.

Who qualifies for each medicine in the UK?

Both medicines share the same core private licensed threshold: adults with a BMI of 30 or above, or 27 or above if a weight-related health condition is present (such as hypertension, type 2 diabetes, high cholesterol or obstructive sleep apnoea). Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. BMI alone does not decide approval, a prescriber weighs the full clinical picture, including current medicines, medical history and contraindications. If you want to think through how either medicine might fit your situation, our guide to choosing between Wegovy or Mounjaro covers the eligibility questions prescribers typically explore.

On the NHS, both medicines are recommended by NICE but under different conditions. Mounjaro (TA1026, December 2024) is being phased into primary care by BMI and comorbidity criteria. Wegovy (TA875, March 2023) is recommended for up to two years within specialist weight management services. Neither pathway is fast; waiting lists are long in most areas. Private treatment through a regulated pharmacy is the route for people who don't qualify for the current NHS cohort or don't want to wait. If the NHS vs private question matters to you, our treatment overview page explains both routes clearly.

Are the side-effect profiles meaningfully different?

Mostly, no. Both medicines share the same dominant side-effect class: gastrointestinal. Nausea, loose stools, constipation, reflux and reduced appetite are common to both, most pronounced in the first weeks after starting or stepping up a dose, and generally settle with time. The slow titration schedule exists largely to manage this. Injection-site reactions, fatigue and headache also appear in both trial populations at similar rates.

Where prescribers sometimes distinguish the two is in the contraception interaction. Tirzepatide slows gastric motility enough that the MHRA advises women taking the oral contraceptive pill to use an additional non-oral method for the first four weeks of treatment and for four weeks after each dose increase. The equivalent caution is not in the semaglutide guidance. Budget is also a common deciding factor, and our guide to whether Mounjaro or Wegovy is cheaper sets out current pricing across doses so you can compare like for like. Both medicines carry a Black Triangle (▼) designation, meaning ongoing safety monitoring by the MHRA. Any suspected side effect can be reported at yellowcard.mhra.gov.uk. Pregnancy, breastfeeding and trying to conceive are contraindications for both; neither is licensed for under-18s.

For a broader side-by-side view of how tirzepatide sits alongside other GLP-1 treatments, our page on Mounjaro vs Ozempic covers how their side-effect profiles and efficacy data compare. The NHS England guidance on weight-management injections covers practical safety points including HRT and surgery.

Which medicine suits you is a clinical decision our prescribers make with you, not something a comparison table can settle on its own. If you are ready to find out which option fits your profile, check your eligibility with a free consultation. You can also explore more detailed questions in our deep-dive on which is better for different situations, or read about our clinical team and how we work.