The different names for Mounjaro and what they all refer to

What the evidence says about tirzepatide before the branding question even arises

The clinical story begins not with a brand but with a molecule. Tirzepatide was studied extensively across the SURMOUNT programme, SURMOUNT-1 alone enrolled 2,539 adults with obesity and no diabetes, and at the 15 mg maintenance level participants lost an average of around 20–21% of body weight over 72 weeks, as published in the New England Journal of Medicine. The SURMOUNT-5 head-to-head trial, also published in the NEJM in 2025, found tirzepatide produced greater average weight reduction than semaglutide 2.4 mg over 72 weeks. Those results belong to the molecule; what changes country to country is what name gets stamped on the pen and what that name is licensed to treat.

The mechanism behind those numbers is worth understanding. Tirzepatide is a dual GIP and GLP-1 receptor agonist, it activates two separate gut-hormone pathways that together reduce appetite, slow gastric emptying and influence blood-sugar regulation. Every name this drug goes by points back to that same mechanism. Our explainer on GLP-1 versus tirzepatide goes deeper on what that dual action means in practice.

Mounjaro, Zepbound and tirzepatide: where each name belongs

Tirzepatide is the international non-proprietary name (INN), the scientific, manufacturer-neutral label that regulators, prescribers and pharmacists use when they want to refer to the compound without reference to any brand. You will see it on prescriptions, in NICE guidance such as TA1026, and in clinical papers.

Mounjaro is Eli Lilly's brand name for tirzepatide in the UK and EU. It holds MHRA authorisation for weight management in adults with a BMI of 30 or above (or 27 or above alongside a weight-related condition such as high blood pressure, high cholesterol or type 2 diabetes), and it also carries a licence for type 2 diabetes. In the UK, Mounjaro arrives as a once-weekly subcutaneous injection via a pre-filled KwikPen in six strengths: 2.5, 5, 7.5, 10, 12.5 and 15 mg. Treatment begins at 2.5 mg (that first strength exists to let the body adjust gradually, not as a therapeutic target) and a prescriber titrates upward from there. For a full picture of how Mounjaro works and what the treatment involves, the Mounjaro overview covers it in detail.

Zepbound is Eli Lilly's brand name for tirzepatide in the United States. It does not exist as a UK product. Zepbound has not been authorised by the MHRA, is not dispensed by any GPhC-registered UK pharmacy, and carries US-specific dosing presentations and pricing that do not apply here. If a UK-based seller offers something called Zepbound, that is a serious red flag, the MHRA has warned publicly about illegally traded and counterfeit weight-loss medicines, and legitimate UK supply chains carry only MHRA-authorised products dispensed on prescription.

Other names you might encounter: retatrutide and the next generation

Some people searching for different names for Mounjaro are actually looking ahead at emerging molecules. Retatrutide is a triple receptor agonist (GIP, GLP-1 and glucagon) developed by Eli Lilly but still in clinical trials. It is not the same compound as tirzepatide and does not yet hold a UK licence for any use. Our comparison of Mounjaro and retatrutide explains what the trial data shows and where the distinction lies, and if you are curious how retatrutide compares head-to-head that analysis is here.

There is also liraglutide, sold as Saxenda for weight management, which is a GLP-1 receptor agonist, different molecule, different receptor profile, daily rather than weekly injection. The liraglutide versus tirzepatide page sets out the clinical differences for anyone weighing up those options.

One timing note worth mentioning: if you are looking into treatment costs across providers and want to compare sensibly, the Mounjaro price guide explains what legitimate private pricing covers and what changed after Eli Lilly adjusted UK list prices in September 2025, worth reading before making a decision, whether you start in January or pick things up after a summer break.

Which name to use when asking about treatment in the UK

In a UK clinical conversation (with a GP, a hospital prescriber or an online service like nume) the correct term is Mounjaro or tirzepatide. Either is understood. Zepbound draws a blank, because it simply does not exist in the UK supply chain. The NHS information on tirzepatide is published under both names, cross-referenced clearly. Any prescriber reviewing your suitability will be working from the Mounjaro SmPC and NICE TA1026 criteria, not US labelling.

At nume, every consultation is reviewed by a GPhC-registered Independent Prescriber, a real clinician reads your answers on the same day. The prescriber decides whether Mounjaro is clinically appropriate for you, documents it correctly, and the prescription is dispensed from nume's own GPhC-registered pharmacy (registration number 9012878, verifiable on the GPhC register). If you are ready to find out whether you're eligible, you can check your eligibility and start your free consultation.