Retatrutide or tirzepatide: how do the two compare right now?

What is retatrutide, and where does it sit right now?

Retatrutide is an investigational medicine developed by Eli Lilly, the same company behind Mounjaro. Where tirzepatide targets two gut-hormone receptors (GIP and GLP-1), retatrutide goes a step further and adds a third: glucagon. This triple-receptor approach earned it the informal label of a "triple agonist". In a phase 2 trial published in the New England Journal of Medicine in 2023, participants taking the highest retatrutide dose lost an average of around 24% of body weight over 48 weeks. That figure drew understandable attention.

What the headline number does not tell you is that phase 2 trials are designed primarily to assess safety signals and find the right dose range, they typically involve a few hundred people over a relatively short window. Phase 3 trials, which test a medicine at scale across thousands of participants, had not reported results at the time this page was written (summer 2026). Retatrutide holds no licence in the UK, the EU or the US. It cannot lawfully be prescribed here. Any seller offering it in the UK is operating outside the licensed supply chain, which is a serious red flag for safety.

There is a misconception that a higher average weight loss in an early trial automatically means a medicine is better. It does not, it means the phase 2 data looks promising. If you are trying to work out whether Mounjaro or retatrutide comes out ahead on current evidence, we cover that comparison in detail. What matters clinically is the full picture from phase 3: sustained efficacy, the side-effect profile at population scale, cardiovascular outcomes, and the prescriber's ability to titrate safely. That picture does not yet exist for retatrutide.

What tirzepatide can actually offer, with evidence to stand behind it

Tirzepatide is licensed in the UK as Mounjaro, and its evidence base is substantial. The SURMOUNT-1 trial randomised 2,539 adults with obesity over 72 weeks; at the 15mg dose, average weight reduction was around 20–21%. The SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, compared tirzepatide directly with semaglutide 2.4mg (Wegovy) in adults with obesity and found tirzepatide produced greater average weight loss. NICE reviewed this evidence and recommended tirzepatide for NHS use in adults meeting specific BMI and comorbidity criteria (TA1026, published December 2024).

That depth of evidence (multiple large trials, a NICE technology appraisal, a published safety profile across thousands of participants, a licensed dose schedule) is what separates tirzepatide from retatrutide at this moment. A prescriber using tirzepatide is working from a known, regulated framework. A prescriber using retatrutide has no such framework to work from, because the medicine is not licensed. For more on how tirzepatide works and what the trials show, we have a dedicated overview.

If you are weighing up Mounjaro versus tirzepatide as separate questions, they are the same medicine; Mounjaro is simply the brand name Eli Lilly uses in the UK. That distinction trips people up surprisingly often.

The decision most UK readers are actually facing

The question "which is better" often conceals the real question, which is: "what weight-loss medicine should I be considering for myself?" Framed that way, the comparison becomes less abstract. Retatrutide is not a choice available to you in the UK today. Tirzepatide is, subject to clinical suitability assessed by a GPhC-registered prescriber.

The useful comparison at this point in time is between tirzepatide and other licensed UK options: how retatrutide relates to Mounjaro more broadly, or how tirzepatide compares to semaglutide (Wegovy). Both are covered in detail elsewhere. For cost context, our guide to Mounjaro pricing in the UK sets out what private treatment actually involves.

If retatrutide reaches a UK licence in future, its licensed dose schedule, contraindications and clinical positioning will be assessed by the MHRA and evaluated by NICE before any regulated service could offer it. Until that happens, pages claiming to supply it are not working from an authorised supply chain. The MHRA has been clear that unlicensed injectable weight-loss medicines carry genuine risk, and reporting concerns to the Yellow Card scheme is always an option.

How to take the next step with a medicine that is actually available

If the evidence behind tirzepatide has convinced you it is worth exploring for your own situation, the route is a clinical consultation. At nume, every consultation is read the same day by a GPhC-registered Independent Prescriber, a real clinician, not a triage algorithm. Eligibility depends on your BMI, your health history and any medicines you are already taking; our prescribers work through that picture with you. There is no referral needed, no waiting list for the private route, and no subscription locking you in. You can also read about all the treatment options we offer before deciding whether to take things further.

Retatrutide may well reach UK patients eventually. For now, the honest answer to "which is better" is that only one of them exists as a lawful, evidenced, clinician-prescribed option here, and that is tirzepatide. Check your eligibility with our prescribers if you would like to explore whether it is right for you.