The main difference between Mounjaro and Wegovy, explained clearly

Step 1: understand the mechanism — one pathway versus two

Wegovy works by mimicking GLP-1, a gut hormone released after eating. It slows how quickly the stomach empties, reduces appetite signals in the brain, and helps regulate blood sugar. That single-pathway action has been well-studied since semaglutide first entered clinical use for type 2 diabetes.

Mounjaro takes the same GLP-1 pathway and adds a second: GIP. GIP is released earlier in the digestive process and appears to amplify the appetite-suppressing effect when both receptors are activated together. It is the only dual-agonist weight-loss medicine currently licensed in the UK, which is why clinical commentary often treats it as a distinct category rather than simply a newer GLP-1. The NHS medicines page on tirzepatide covers the dual-receptor mechanism in accessible detail if you want to read further.

For most people this distinction is not an abstract point. The dual mechanism appears to translate into a meaningful difference in average weight loss, as the trial evidence in step two shows.

Step 2: look at what the evidence actually says about weight loss

Clinical trials give the clearest comparison, though no two trials are identical in design, so direct head-to-head results carry the most weight.

In the SURMOUNT-1 trial (2,539 adults with obesity, 72 weeks), tirzepatide produced an average body-weight reduction of around 20–21% at the 15mg maintenance dose. The STEP 1 trial for semaglutide 2.4mg (68 weeks) reported an average reduction of around 15%. Both figures come from placebo-controlled trials and are cited in the respective NICE appraisal of tirzepatide (TA1026) and the NICE appraisal of semaglutide (TA875).

The most direct comparison comes from SURMOUNT-5, a head-to-head open-label trial published in the New England Journal of Medicine in 2025. Across 72 weeks and 751 adults with obesity and no diabetes, tirzepatide produced greater average weight reduction than semaglutide 2.4mg. If you are weighing up these two options, our page on what the difference between Wegovy and Mounjaro actually means in practice walks through the trial findings in plain terms. The gap narrowed when Novo Nordisk's higher 7.2mg semaglutide dose was modelled, though that dose is newer and long-term head-to-head data at 7.2mg are still emerging.

The comparison table below summarises the key factual differences:

A note on Ozempic: it contains the same active ingredient as Wegovy (semaglutide) but is licensed for type 2 diabetes, not weight management. It is not a route to weight-loss treatment. The difference between Ozempic and Mounjaro is worth reading if you have seen Ozempic mentioned in this context.

Step 3: match eligibility and side-effect profile to your situation

Both medicines share a broadly similar side-effect profile, because both slow gastric emptying. Nausea, loose stools, constipation, reflux and fatigue are the most commonly reported effects, typically peaking after starting or after a dose step, then settling over days to a couple of weeks. Injection-site reactions are possible with either. The NHS semaglutide page and the tirzepatide equivalent list these in full.

One practical difference worth knowing: women using oral contraceptives who start Mounjaro are advised to add a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide can reduce pill absorption. Current evidence does not show the same effect with semaglutide. Anyone on oral contraception should raise this with their prescriber before starting either treatment.

Eligibility thresholds are set per licence and per NICE guidance. Lower BMI thresholds apply for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds under UK guidance, the relevant detail is on our weight-loss treatments overview. BMI is one part of the picture; your prescriber also considers your medical history, current medicines, and any conditions that affect suitability.

Neither medicine is recommended during pregnancy, breastfeeding, or if you are trying to conceive. Neither is licensed for under-18s. History of certain thyroid conditions or pancreatitis requires a careful prescriber discussion before either is considered.

Step 4: how to make a decision that is actually right for you

Reading a comparison table is a reasonable starting point. It is not the endpoint. The question of which treatment suits you depends on factors a table cannot hold: your weight-loss history, any medicines you already take, your BMI, your health conditions, and your own preferences about treatment. A lot of people come to us having already decided, and occasionally the prescriber agrees straight away. Sometimes the conversation surfaces a reason to try the other option first.

At nume, a named prescriber reads every consultation on the same day it is submitted. There is no automated triage, no algorithm that green-lights your application. If you place your order by noon on a working day and are clinically approved, your treatment is dispatched that afternoon and delivered free by DPD the next working day. Our clinical team's approach is set out on the clinical team page if you would like to know more before starting.

For a fuller side-by-side read, the Wegovy vs Mounjaro comparison and the cost comparison between the two cover those angles in more depth. If you are still working out which option fits your circumstances, our guides on the difference between Mounjaro and Wegovy and on how the Mounjaro and Wegovy difference plays out clinically go into greater detail on the points that matter most for that decision. Which suits you is a clinical decision our prescribers make with you.