How Wegovy Differs from Mounjaro: Mechanism, Results and What to Expect

Do Wegovy and Mounjaro work the same way inside your body?

The short answer is no, and the difference is clinically relevant. Wegovy contains semaglutide, a GLP-1 receptor agonist. It mimics a hormone released after eating, signalling fullness to the brain, slowing how quickly food leaves the stomach, and reducing appetite. That single pathway has been studied extensively: the STEP 1 trial, published in the New England Journal of Medicine, found an average body-weight reduction of around 15% over 68 weeks at the 2.4mg maintenance dose.

Mounjaro contains tirzepatide, which binds to both GLP-1 and GIP receptors. GIP is a separate gut hormone involved in fat metabolism and energy balance. Activating both pathways together appears to produce a stronger appetite-suppressing effect than either alone. In the SURMOUNT-1 trial, average weight loss at the highest dose reached around 20–21% over 72 weeks. If you want to understand exactly how tirzepatide differs from semaglutide at a molecular and clinical level, we cover that in detail separately. The SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, directly compared tirzepatide against semaglutide 2.4mg and found greater average weight reduction with tirzepatide over 72 weeks.

One important nuance: Wegovy now has a 7.2mg dose option, approved by the MHRA in April 2026, which produced around 20.7% average weight loss in trials — narrowing the gap considerably. You can read a more detailed breakdown of how Wegovy and Mounjaro compare across their mechanisms, doses, and trial results if that level of detail helps.

Are the eligibility criteria and licensed uses the same for both?

They are broadly similar but not identical. Both medicines are licensed in the UK for weight management in adults with a BMI of 30 or above, or a BMI from 27 upwards alongside at least one weight-related health condition such as high blood pressure, type 2 diabetes or high cholesterol. Lower BMI thresholds apply for certain ethnic backgrounds under UK clinical guidance. Neither is licensed for use in pregnancy, breastfeeding or for people under 18.

Where they differ most clearly is in NICE's recommendation criteria for NHS access. NICE recommends tirzepatide (TA1026, published December 2024) for adults with a BMI of 35 or above alongside at least one qualifying comorbidity, through a phased NHS rollout. Semaglutide under Wegovy is covered by NICE guidance TA875, but with a stricter requirement: it should be used for a maximum of two years and only within a specialist weight management service. No equivalent two-year cap applies to tirzepatide under TA1026.

One point worth flagging: Ozempic is also semaglutide, but it is licensed for type 2 diabetes management, not weight loss. The same applies to Rybelsus tablets. Only Wegovy carries a UK weight-management licence for semaglutide. Our page on how Mounjaro and Ozempic differ covers that distinction in full.

How do the side-effect profiles compare in practice?

Both medicines share a broadly similar side-effect profile because they share the GLP-1 mechanism. Nausea, loose stools, constipation, indigestion, and fatigue are the most commonly reported effects for both. These tend to be most noticeable in the early weeks or after a dose increase, and they frequently settle as the body adjusts.

The NHS medicines information pages for tirzepatide and semaglutide list these in detail, along with rarer but more serious effects that require prompt medical attention: severe or persistent stomach pain that extends to the back (a possible sign of pancreatitis), gallbladder symptoms, and signs of a serious allergic reaction. Both carry a Black Triangle (▼) designation from the MHRA, meaning they are subject to additional post-market monitoring. Suspected side effects from either medicine can be reported at yellowcard.mhra.gov.uk.

One practical difference: tirzepatide's absorption of oral medicines, including the contraceptive pill, may be reduced in the first four weeks of treatment and after each dose increase. Women taking oral contraceptives are advised to use an additional barrier method during those windows. No equivalent interaction data exists for semaglutide. If you are considering switching from one medicine to the other, our page on moving from Mounjaro to Wegovy outlines what that process involves clinically.

How do the two medicines compare side by side?

These figures come from separate clinical trials with different participant populations and durations, so they are not a direct head-to-head comparison except where SURMOUNT-5 is cited. Numbers are trial averages; individual results vary. If you would like a fuller picture of the key differences between Wegovy and Mounjaro, that page sets them out in detail. The cost side of this question is covered on our page comparing whether Mounjaro or Wegovy is cheaper. For a broader look at available treatments, our treatment overview may help orient you. Deciding which medicine is right for you is a clinical judgement — one our prescribers work through with you during your consultation, drawing on your full health history, not just these numbers.