Tirzepatide vs Mounjaro: what's the difference, and does it matter?

There is no 'tirzepatide vs Mounjaro' choice, but there is a real comparison worth making

Mounjaro is tirzepatide. Eli Lilly holds the UK marketing authorisation under the brand name Mounjaro; the medicine inside every pre-filled KwikPen is tirzepatide. You will sometimes see 'tirzepatide' used in NICE guidance, clinical trial papers and prescribing references precisely because those documents refer to the molecule rather than the brand, but when a UK pharmacy dispenses it, it comes as Mounjaro.

The comparison that genuinely helps readers is tirzepatide (Mounjaro) measured against semaglutide (Wegovy), the other licensed injectable weight-loss medicine in the UK. That's covered in depth on our tirzepatide vs Mounjaro for weight loss page, which walks through the head-to-head trial evidence. If you've seen the name 'Zepbound' online, that is the US brand name for tirzepatide, it does not exist as a UK product and is not available from any UK pharmacy. You may also have come across questions about whether tirzepatide and Manjaro are the same thing, and that page explains the distinction clearly.

Tirzepatide is also distinct from retatrutide, a triple-agonist medicine still in clinical trials, and if you want to understand how these two molecules differ, our detailed look at retatrutide vs tirzepatide sets out where that research currently stands, with our comparison of reta vs tirzepatide exploring the same question from a different angle.

What the clinical trial evidence shows for tirzepatide

Because Mounjaro is tirzepatide, every piece of trial evidence applies equally to both names. The SURMOUNT-1 trial (2,539 adults with obesity, followed for 72 weeks) reported an average body-weight reduction of around 20–21% at the 15mg dose, with some analyses reaching approximately 22.5%. Those are the figures NICE cited when recommending tirzepatide in Technology Appraisal 1026, published December 2024.

In the SURMOUNT-5 open-label trial (72 weeks, 751 adults), tirzepatide produced greater average weight loss than semaglutide 2.4mg, the most direct head-to-head comparison available to date, published in the New England Journal of Medicine in 2025.

Tirzepatide works by activating two gut-hormone receptors (GIP and GLP-1) simultaneously, which is why it is sometimes called a dual agonist. This distinguishes it from semaglutide, which acts on GLP-1 receptors only. The practical upshot, based on current trial data, is that tirzepatide tends to produce somewhat greater average weight reduction. Whether that difference matters for any individual depends on their health picture, not on a league table.

Comparing the two licensed injectable weight-loss medicines side by side

The table below sets out the key factual differences between tirzepatide (Mounjaro) and semaglutide (Wegovy injection) as licensed for weight management in the UK. Numbers are drawn from the respective NICE technology appraisals and published trial data.

A quick note on Ozempic: it also contains semaglutide but is licensed for type 2 diabetes, not weight management. It should never be presented as an alternative to Wegovy for weight loss. Our page on GLP-1 medicines vs tirzepatide goes further on the mechanistic differences if you want that detail.

How the prescription process works, and how to choose

Neither tirzepatide nor semaglutide is available without a prescription. The decision between them isn't one to make based on a comparison table alone; it sits with a prescriber who can weigh up your medical history, current medicines and preferences.

At nume, every consultation is reviewed the same day by a prescriber on our clinical team. If you're curious about who that is, you can read more about our clinical oversight. The NICE guidelines for Mounjaro are also publicly available and worth understanding before your consultation, they explain the thresholds used by NHS services, which differ from private eligibility criteria.

There's no bad time to start a consultation, though a Monday order before 12pm is a straightforward way to have treatment dispatched and in your hands by Tuesday, which some people find neatly fits around a payday. Our treatment page has current information on both medicines we dispense. If you want a broader look at options, the weight-loss overview is a good starting point.

Which medicine suits you is a clinical decision our prescribers make with you, not something a webpage can settle. Start your free consultation and let a real clinician give you a considered answer.