Is Retatrutide Stronger Than Semaglutide? What the Trial Data Shows

What retatrutide is and why the phase 2 results attracted attention

Retatrutide is an investigational medicine developed by Eli Lilly that acts on three hormone receptors simultaneously: GIP, GLP-1 and glucagon. That triple action is the reason researchers expected it to outperform existing dual and single agonists. In a phase 2 trial published in the New England Journal of Medicine in 2023, adults with obesity who received the highest retatrutide dose lost an average of around 17% of body weight at 24 weeks and up to approximately 24% at 48 weeks. Those numbers generated genuine excitement in obesity medicine. They were, at the time, higher than anything a licensed medicine had produced in a similarly designed trial.

The important qualification is what phase 2 means. These trials typically enrol a few hundred participants over months, primarily to establish safety signals and find the right doses before larger work begins. They are not powered to give the kind of certainty a regulator needs before granting a licence. The phase 3 TRIUMPH programme is now underway, and results are expected in the next few years. Until those are published and reviewed, retatrutide sits firmly in the category of promising rather than proven at scale.

For UK readers weighing up options, the practical point is straightforward: you cannot be prescribed retatrutide in the UK today, regardless of how the early numbers look. Our clinical team at nume keeps a close eye on the pipeline, but we can only offer what is licensed and safe to dispense.

How semaglutide's evidence base actually stands up

Semaglutide's phase 3 data comes from the STEP programme, a series of large, rigorous trials. STEP 1, published in the New England Journal of Medicine, enrolled 1,961 adults with obesity over 68 weeks and found an average body-weight reduction of around 15% at the 2.4mg weekly dose alongside lifestyle support. That is a substantial, replicated finding from a trial population large enough to give regulators confidence, which is why the MHRA licensed Wegovy for weight management and NICE subsequently appraised it.

Since then, semaglutide's evidence has grown further. The MHRA approved a higher 7.2mg maintenance dose of Wegovy in January 2026, with a dedicated single-dose pen following in April 2026. Trials at that dose have reported average losses of around 20.7% over 72 weeks, narrowing the gap with tirzepatide and making semaglutide a genuinely competitive option even as the pipeline matures. You can read a fuller breakdown of how Wegovy compares to other currently licensed medicines on our Wegovy versus Saxenda comparison page.

The clinical story for semaglutide is also broader now than weight management alone. The MHRA granted conditional approval in July 2026 for Wegovy to treat MASH, a form of fatty liver disease, a signal of how the evidence base continues to develop after initial licensing.

Why the comparison is harder than the headline numbers suggest

Placing a 24%-at-48-weeks retatrutide figure next to a 15%-at-68-weeks semaglutide figure looks like a clean contest. It is not. The trials ran for different durations, used different populations, measured outcomes at different timepoints and were designed with different primary goals. Phase 2 populations tend to be more tightly selected, which can amplify results. Weight loss also typically continues past 48 weeks when treatment carries on, so the retatrutide figure may not reflect a plateau.

The only genuinely controlled head-to-head comparison published so far in this class pitted tirzepatide against semaglutide 2.4mg: the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, found tirzepatide produced greater average weight reduction. Tirzepatide is a dual agonist, not a triple one, and it is licensed in the UK right now as Mounjaro, available through a private prescription following clinical assessment. If you are curious how that compares with Wegovy more specifically, our semaglutide fact sheet sets out the numbers clearly.

A question our prescribers hear fairly often is whether waiting for a more powerful medicine makes sense. Clinically, there are real costs to deferring treatment that is available now and licensed for your situation. Body weight is not a static backdrop while the trial data accumulates.

What this means if you are considering your options today

For anyone in the UK right now, the realistic choice is between licensed medicines: semaglutide as Wegovy and tirzepatide as Mounjaro. Both are prescription-only medicines requiring a clinical assessment before a prescriber can decide whether either is appropriate for you. Retatrutide is not on that list yet, and there is no clear timeline for UK licensing. If it does reach that stage, it will require the same regulatory scrutiny and prescriber oversight as anything else in this class.

Questions about which currently licensed option suits you are worth exploring properly, not through trial headlines. If you want a broader look at what medicines produce greater weight loss than semaglutide among those already licensed, that page covers the current picture. The semaglutide overview is a good starting point if you want the full clinical picture on Wegovy before a consultation. And if cost is part of your thinking, our Wegovy price comparison page explains what a legitimate private prescription typically includes, because the tablet-vs-injection choice, and the cost of each, matters practically. Many people find it useful to read that before their consultation, rather than arriving with a figure from a forum.

Speaking to a prescriber is the only way to move from the research phase to a treatment plan. If you'd like to do that, speak to our prescribers through a free consultation, reviewed the same day by a GPhC-registered clinician, not a chatbot.