Is Retatrutide Better Than Mounjaro for Weight Loss?

The mechanism gap: why retatrutide looks more potent on paper

Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, it targets two gut-hormone pathways involved in appetite regulation and blood-sugar control. That dual action is already what sets it apart from older single-pathway treatments. Retatrutide goes a step further: it is a triple agonist, activating GIP, GLP-1 and glucagon receptors simultaneously. The glucagon component is thought to increase energy expenditure as well as reduce appetite, which is the theoretical basis for the larger weight-loss numbers seen in early trials.

In a phase 2 study, participants on the highest retatrutide dose lost roughly 24% of body weight over 48 weeks. That figure has attracted significant attention. But phase 2 trials are designed to test safety and find the right dose range, they are not powered to give the kind of definitive efficacy data that phase 3 programmes produce. The SURMOUNT programme for tirzepatide involved thousands of adults across multiple large trials before NICE recommended it in December 2024. Retatrutide has not reached that stage. If you want to understand whether retatrutide or Mounjaro is the better option, including what the trial data does and does not tell us, the comparison is more nuanced than the headline numbers suggest. Whether retatrutide is better than tirzepatide in a real, head-to-head sense remains genuinely unknown.

For now, a practical check worth doing: look up the MHRA's register at GOV.UK's medicine licensing checker, retatrutide does not appear there because it has not been authorised for use in the UK.

What the numbers actually show, and where the comparison breaks down

The table below summarises what the published evidence says, without overstating it.

The headline trial figures suggest retatrutide may produce greater average weight loss. That is worth knowing. It is equally worth knowing those numbers come from a small phase 2 study while tirzepatide's come from a large phase 3 programme scrutinised by NICE and the MHRA. You can explore how Mounjaro works and what its UK evidence base looks like in more detail.

The only treatment you can actually access in the UK today

Retatrutide is not available, from nume, from any UK pharmacy, or from any clinic. It does not have UK marketing authorisation. Anyone offering it in the UK would be doing so outside the licensed supply chain, which is a significant safety concern. The MHRA's Yellow Card reporting tool exists partly for exactly this situation: reports of medicines being supplied without proper authorisation help regulators act.

Mounjaro, meanwhile, is licensed, NICE-recommended, and available now through a private prescription following a clinical assessment. If the question is which of the two you should take, the answer is straightforward: retatrutide is not a live option. If the question is whether it might eventually prove to be better than tirzepatide, the honest answer is that the early signals are interesting but the evidence needed to say so definitively does not yet exist.

People sometimes arrive at this question because they want the strongest treatment available. That instinct makes sense. The right question to ask a prescriber is not which molecule has the highest phase 2 number, but which licensed treatment suits your health profile, your history and your goals. Our pages on what the evidence says about treatments compared to Mounjaro and on the GLP-1 medicines stacked up against tirzepatide cover the licensed landscape in more depth.

Which is better for you? That's a clinical question, not a trial-data question

Even if retatrutide were licensed tomorrow, whether it would be the right choice for a given person would still depend on individual factors: BMI, comorbidities, medication history, how well they tolerate GI side effects, practical considerations like injection frequency and storage. Tirzepatide is not a consolation prize. Its trial results are among the strongest ever recorded for a licensed weight-loss medicine, and for people who respond well, the outcomes are substantial. A clinician reviewing your full picture is better placed to make that call than a comparison of phase 2 percentages.

At nume, every consultation is read by a GPhC-registered Independent Prescriber, you can read more about our clinical team and how the process works. If you are considering Mounjaro and want to understand whether it is appropriate for you, the clearest next step is a consultation rather than further comparison of medicines that are not yet available. Some patients also ask about how Nevolat compares to Mounjaro, which is worth reading if you are weighing up the licensed options currently on the market. See our detailed breakdown of retatrutide versus Mounjaro if you want to go deeper into the trial data, or our treatment options overview to start a free consultation today.