Tirzepatide compared to Mounjaro: what's actually different?

You searched 'tirzepatide vs Mounjaro', here's why that search is confusing

Picture the moment it clicked for someone who'd spent an evening cross-referencing trial papers with pharmacy websites. The SURMOUNT-1 results kept referencing 'tirzepatide'. Mounjaro was on the pharmacy page. Were these competing treatments? No. Tirzepatide is the International Non-proprietary Name, the molecule's scientific label. Mounjaro is what Eli Lilly printed on the box. Every Mounjaro KwikPen contains tirzepatide; every SURMOUNT trial studied the same compound you'd be injecting. If you want to understand exactly why the two names refer to the same thing, our page comparing tirzepatide and Mounjaro explains the relationship clearly, and the short answer is: there's no meaningful gap between the two names. The full Mounjaro overview on our site covers what's inside the pen in detail.

Where genuine comparison questions do arise is when people mean to ask how tirzepatide (Mounjaro) compares to semaglutide (Wegovy), or to older treatments like liraglutide. That's a fair question and the trial evidence does give us something to work with, which is why the sections below address it. If you arrived here after seeing the word 'Zepbound', that's worth clarifying too: Zepbound is the US brand name for tirzepatide and is not available in the UK. In the UK, tirzepatide is Mounjaro, full stop.

What makes tirzepatide's mechanism different from a standard GLP-1

Most weight-loss injections approved in the UK act on a single receptor, the GLP-1 receptor, which plays a role in appetite signalling and slowing gastric emptying. Tirzepatide (Mounjaro) activates two receptors: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). GIP is thought to work alongside GLP-1 in ways researchers are still characterising, but the practical result (seen in trials) is that the dual action produces greater average weight reduction than GLP-1 agonism alone at comparable doses. The comparison between GLP-1 medicines and tirzepatide goes into this mechanism in more depth if you want to understand the receptor biology before speaking to a prescriber.

In the SURMOUNT-1 trial, published in the New England Journal of Medicine, adults with obesity who received tirzepatide 15mg lost around 20–21% of their body weight on average over 72 weeks alongside a reduced-calorie diet and increased activity. That's a figure worth holding lightly (clinical-trial conditions, motivated participants, and individual results vary) but it gives a factual baseline. SURMOUNT-1 randomised 2,539 participants; the wider tirzepatide clinical programme across SURPASS and SURMOUNT combined over 10,000 people.

The head-to-head data matters too. In the SURMOUNT-5 trial (72 weeks, 751 adults with obesity, published in the New England Journal of Medicine in 2025), tirzepatide produced greater average weight reduction than semaglutide 2.4mg. If you want to understand how tirzepatide compares to Manjaro, that page walks through those numbers alongside what they mean in practice. Neither trial can tell your prescriber which medicine is right for you specifically.

Tirzepatide vs semaglutide: a factual comparison

The table below captures the key factual differences between tirzepatide (Mounjaro) and semaglutide (Wegovy), the two GLP-1-class weight-loss injections currently licensed in the UK for weight management. Numbers from published trials are cited; everything else reflects current UK licensing and NICE guidance.

A note on Ozempic: Ozempic is also semaglutide but holds a UK licence only for type 2 diabetes, not weight management. It should not be prescribed as a weight-loss medicine, and NICE's weight-management guidance does not apply to it. Saxenda (liraglutide) versus Mounjaro is a separate question worth reading if liraglutide has come up in your research.

Who each medicine is licensed for, and how a prescriber chooses

Both tirzepatide and semaglutide share broad eligibility criteria: adults with a BMI of 30 or above, or 27 or above where at least one weight-related condition is present (such as high blood pressure, high cholesterol, type 2 diabetes, or obstructive sleep apnoea). Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. Cost is often what people compare first, but eligibility and clinical suitability are what a prescriber weighs.

The side-effect profiles of both medicines are broadly similar, nausea, constipation, indigestion and fatigue are most commonly reported, typically most noticeable when starting or after a dose step. Individual tolerance varies, and the prescriber's job is partly to judge which medicine and which titration pace suits your history. NICE's appraisal of tirzepatide (TA1026) and TA875 for semaglutide set out the clinical basis for both recommendations in full.

If you're already on one treatment and wondering about the other, that's a conversation for your prescriber, not a website. Which suits you is a clinical decision, one our prescribers make with you, not for you, after reviewing your full picture. When you start your consultation with nume, your answers go to a named clinician the same day; if approved, your pen ships from our GPhC-registered UK pharmacy and arrives with DPD tracked delivery the next working day, in a plain box that gives nothing away. You can explore the full range of weight-loss treatments we offer or read more about how medical weight management works before you decide.