How similar are Mounjaro and Wegovy, really?

Two medicines, one shared goal — but a different receptor story

Both Mounjaro (tirzepatide, made by Eli Lilly) and Wegovy (semaglutide, made by Novo Nordisk) work through the gut-hormone system. Wegovy activates GLP-1 receptors, which signal fullness, slow the stomach and moderate blood-sugar response. It does one thing and does it well. Mounjaro goes further: it activates both GLP-1 and GIP receptors simultaneously, making it the only dual-agonist weight-loss medicine currently licensed in the UK. That second receptor pathway appears to amplify the appetite-suppressing effect, and the trial numbers reflect that.

This distinction matters clinically. Because the receptor targets differ, the two medicines are not interchangeable in any simple sense, even though patients often ask how Wegovy and Mounjaro stack up directly. Some people do switch between them, you can read more about moving from Mounjaro to Wegovy or the process of switching in the other direction in our dedicated guides. Any switch needs a prescriber's involvement, not a self-directed adjustment.

What the clinical evidence actually shows

Both medicines have robust phase-3 trial programmes behind them. SURMOUNT-1, published in the New England Journal of Medicine, reported an average body-weight reduction of around 20–21% at the 15mg tirzepatide dose over 72 weeks in adults without diabetes. The STEP 1 trial for semaglutide 2.4mg, also in the NEJM, found an average reduction of around 15% over 68 weeks. More directly, the SURMOUNT-5 head-to-head trial (72 weeks, 751 adults with obesity, no diabetes) found that tirzepatide produced greater average weight loss than semaglutide 2.4mg, a conclusion that influenced NICE's committee discussions. These are averages from trial populations; individual results vary.

It is also worth knowing that Wegovy now has a 7.2mg maintenance dose, approved by the MHRA in January 2026 and available as a dedicated single-dose pen from April 2026. Early data puts average loss at around 20.7% at that dose, narrowing the gap with tirzepatide's top dose. The comparison is genuinely closer at the higher end than the earlier headline numbers suggested. Cost differences between the two are another factor worth looking at once you have a clinical picture.

One detail about what actually arrives is worth mentioning: your pen comes in plain, unbranded packaging via DPD (nothing on the outside gives away its contents) and you can track it on your phone before it reaches your door.

Do Mounjaro and Wegovy suit the same people?

The licensed eligibility criteria are closely aligned. Both are for adults with a BMI of 30 or above, or 27 and above alongside at least one weight-related condition such as high blood pressure, raised cholesterol, obstructive sleep apnoea or type 2 diabetes. Under UK guidance, lower BMI thresholds apply for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds. Neither medicine is licensed for people under 18, and neither is recommended during pregnancy, breastfeeding or when trying to conceive.

NICE's NHS recommendations differ in their detail: NICE TA1026 for tirzepatide and NICE TA875 for semaglutide both set out specific criteria for NHS access, including comorbidity thresholds and service requirements. In practice, NHS access remains limited and phased; private treatment through a regulated pharmacy is the main route for most people at the moment. On the side-effect profile, both medicines share a GI-led pattern: nausea, loose stools, constipation and indigestion are the most commonly reported effects, most noticeable at the start of treatment or after a dose step up, and typically settling within a couple of weeks for most people. There are some specific differences, for instance, women taking oral contraceptives alongside tirzepatide 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 pill absorption may be reduced. For semaglutide, NHS guidance does not flag the same concern. It is a detail worth discussing at consultation, which is exactly why the comparison between these two is a clinical conversation rather than a checklist exercise.

Which one is right for you?

There is no universal answer, and any page that gives you one is simplifying things beyond usefulness. The trial evidence favours tirzepatide on average weight loss, particularly at higher doses. But average results from a trial population do not predict your individual response, and other factors matter too: your medical history, any medicines you already take, how you feel about injections at different dose stages, and what your prescriber finds when they review your full picture. Some people do better on one than the other; some switch and find the change helpful. You can explore what choosing between Wegovy and Mounjaro actually involves, or read a fuller side-by-side on our Wegovy vs Mounjaro comparison page. Our clinical team, led by our lead prescriber, reviews every consultation personally. Which one suits you is a clinical decision our prescribers make with you.

Speak to our prescribers, the consultation is free, and there is no obligation to proceed.