Mounjaro®
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Start journey Learn moreRetatrutide vs Semaglutide: the evidence, the licensing gap, and your current options
Why the switch isn't possible yet, and what retatrutide actually is
Retatrutide is an investigational triple receptor agonist developed by Eli Lilly, targeting GIP, GLP-1 and glucagon receptors simultaneously. That triple mechanism is distinct from semaglutide's single GLP-1 pathway and from tirzepatide's dual GIP/GLP-1 approach. Phase 2 trial data published in the New England Journal of Medicine reported average weight reductions of up to around 24% over 48 weeks at the highest doses, figures that attracted considerable clinical interest. Phase 3 trials are ongoing as of mid-2026.
The key regulatory fact: the MHRA has not approved retatrutide for any indication in the UK. There is no licensed product, no approved dose, no legitimate UK prescriber who can write that prescription today. Any seller claiming to offer it is operating outside the law, and the MHRA has been clear about the risks of medicines obtained through unlicensed channels. You can report suspect sellers through the Yellow Card scheme if you encounter them. If you're considering how to switch from semaglutide to retatrutide, the honest framing is: you're making a decision about the future, not the present.
For a fuller breakdown of the trial data and the mechanism differences, the retatrutide vs semaglutide comparison covers those details specifically.
How semaglutide and retatrutide compare on the evidence available
Comparing licensed and unlicensed medicines side by side requires some care. The figures below are from separate trials with different populations, durations and designs, they are not a head-to-head, and should not be treated as one. What they show is the landscape, not a verdict.
| Factor | Semaglutide 2.4mg (Wegovy) | Retatrutide (investigational) |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | GIP, GLP-1 and glucagon receptor agonist (triple) |
| Average weight reduction in trials | ~15% over 68 weeks (STEP 1, NEJM, 2021) | Up to ~24% over 48 weeks (phase 2, NEJM, 2023)) phase 3 ongoing |
| UK licensed for weight management | Yes (Wegovy, MHRA-approved | No) not licensed in the UK |
| Available on UK private prescription | Yes | No |
| Dosing frequency | Once weekly injection | Once weekly injection (in trials) |
| NICE recommended (weight management) | Yes (TA875 | Not applicable) not licensed |
Semaglutide's trial evidence comes from the large STEP programme, including STEP 1 published in the New England Journal of Medicine, which involved nearly 2,000 adults. Retatrutide's phase 2 data are genuinely promising, but phase 2 trials involve far smaller populations and shorter follow-up; the phase 3 programme will determine whether those results hold at scale. Until that data exists and regulators review it, any comparison of efficacy should be read as preliminary.
The decision you're actually facing: wait, or act on what's licensed now
If you're already on semaglutide and wondering whether to switch from semaglutide to retatrutide, the practical question resolves into two scenarios. Either you're doing well on semaglutide and curious whether something better is coming, or you're not getting the results you hoped for and wondering whether there's an alternative worth pursuing now.
For the first scenario: staying on a treatment that is working, with a licensed medicine and a prescriber monitoring your progress, is clinically reasonable. Retatrutide's timeline to UK approval is not publicly confirmed; waiting for an unlicensed product means pausing progress that may otherwise continue.
For the second scenario: there is already an alternative licensed in the UK. Tirzepatide (Mounjaro), a dual GIP and GLP-1 receptor agonist, produced greater average weight loss than semaglutide 2.4mg in the SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025. For patients who haven't achieved what they hoped on Wegovy, the question of whether retatrutide would outperform is currently unanswerable in the UK; what can be answered is whether tirzepatide suits you better. A quick check worth doing: look up the NHS semaglutide medicines page to see the full list of conditions where the current treatment isn't recommended, then bring those specifics to a prescriber conversation.
If you've already considered those options and want to understand exactly how a switch from semaglutide to retatrutide would work when licensing changes, that page covers the process question in detail. Separately, if you're weighing Wegovy against other semaglutide-based products, the Wegovy vs Ozempic page clarifies the licensing distinction, Ozempic carries a diabetes licence, not a weight-management one.
The most useful thing a prescriber can do right now is review your current treatment, your results to date, and whether a licensed alternative is worth exploring. That's a clinical conversation, not one this page can resolve. Which option suits you is a decision our prescribers make with you, based on your full picture.
You can explore your options and check your eligibility through our free consultation. If you'd like background on what's currently licensed and dispensed by nume (sorry, by nume) the weight-loss treatments overview sets that out clearly, and if you want to see how orforglipron compares to semaglutide as another pipeline option worth knowing about, that comparison is there too.
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