Home / Compounds / Retatrutide
Retatrutide
Triple receptor agonist · No brand name. Development code LY3437943
- UK status
- Not licensed anywhere
- Availability
- Clinical trials only
- Evidence base
- Phase 3 ongoing
- Controlled drug
- No
Sequence
Sequence not published in full. Verify against the trial literature before publishing one.
The short version
What it does
In trials, reduces appetite more than anything else in this class so far.
How it does it
Where semaglutide copies one of your body's after-meal signals and tirzepatide copies two, this copies three. The third one is meant to make you burn slightly more energy as well as eat less.
The catch
It is not finished. No country has approved it, so nobody independent has yet decided whether the benefits are worth the risks. Everything sold online under this name is illegal and unverifiable.
Everything below goes into the detail, with sources.
Retatrutide is the next step in the same direction: instead of one or two hormone receptors, it targets three. It also has no marketing authorisation in any country, which has not stopped it being sold online.
At a glance
- Compound type
- Peptide
- Drug class
- Triple agonist, GLP-1, GIP and glucagon receptors
- Route
- Injection under the skin, in trials
- Frequency
- Weekly, in trials
- Originator
- Eli Lilly
- Development code
- LY3437943
- Approval status
- None, anywhere in the world
- In sport
- Unapproved, so would fall under WADA S0. Verify with UKAD.
01What it is
Retatrutide is an investigational peptide developed by Eli Lilly. It acts on the GLP-1 and GIP receptors, like tirzepatide, and adds a third target, the glucagon receptor.
Activating the glucagon receptor is the interesting part, because glucagon raises blood glucose, which sounds like the wrong direction for a diabetes drug. The rationale is that it also increases energy expenditure, and that the combination with the other two receptors produces a net metabolic benefit. Whether that theory holds up is precisely what the trials are testing.
02How it came about
Retatrutide is the current end point of a clear progression: one receptor, then two, now three. Adding the glucagon receptor was the counterintuitive step, because glucagon raises blood glucose, which is the opposite of what a diabetes drug should do. The rationale is that it also increases energy expenditure, and that in combination the net effect is beneficial.
Phase 2 results generated substantial attention. The phase 3 TRIUMPH programme is ongoing, with regulatory submission publicly discussed for late 2026 and any UK licence later than that.
03UK legal and licensing status
Retatrutide has no marketing authorisation from the MHRA, the EMA or the FDA. It cannot be lawfully prescribed or supplied for human use in the UK. The only lawful route to receiving it is enrolment in an authorised clinical trial, which you can search for through the NIHR Be Part of Research portal.
Anything sold as retatrutide outside a trial is grey-market product. Sellers commonly label it "research use only" and publish dosing tables alongside, which is the contradiction the MHRA has been examining. Identity, purity and concentration are unverifiable regardless of what certificate accompanies it.
04How it works
- GLP-1 receptor. Insulin release, slower gastric emptying, reduced appetite.
- GIP receptor. Further insulin effect, plus action on fat tissue.
- Glucagon receptor. Intended to raise energy expenditure. This is the novel element and the main source of uncertainty about long-term effects.
05What it is not
Claims that attach themselves to this compound and do not hold up.
- Not a licensed medicine anywhere. Not approved, not prescribable, not lawfully supplied for human use in any country.
- Not what grey-market sellers are shipping. Whatever is in an unlicensed vial is unverifiable in identity, purity and concentration, whatever certificate comes with it.
- Not proven superior. Phase 2 figures circulate widely as though settled. The phase 3 record is incomplete and no regulator has yet weighed benefit against risk.
06What the evidence shows
Phase 2 results reported substantial weight change and generated most of the public interest. The phase 3 programme, TRIUMPH, is ongoing, with regulatory submission publicly discussed for late 2026 and any UK licence realistically later than that. NICE appraisal and NHS availability would follow separately.
Treat any specific percentage you see quoted for retatrutide with care. Much of what circulates comes from phase 2 data, interim readouts, or press coverage rather than published phase 3 results.
This is a drug in development. Long-term safety is not established, the phase 3 record is incomplete, and no regulator has yet assessed the balance of benefit and risk. That is not a gap that a certificate of analysis or an online review closes.
07Reported harms
Reported effects in trials have been dominated by the same gastrointestinal pattern as the rest of the class. Because the compound is unlicensed, there is no Summary of Product Characteristics and no approved patient information leaflet, which means no authoritative frequency table exists.
Separately, illicit supply has been linked to harm. Reporting during 2026 has described enforcement activity in the UK and a sharp rise in poison centre contacts in the United States relating to grey-market weight-loss peptides.
08Interactions and cautions
No licence means no SPC and no authoritative interaction list. Trial protocols manage interactions under clinical supervision, which is precisely what someone buying it online does not have.
09Stopping
Unknown outside trial conditions. There is no published guidance on stopping because there is no approved use to stop.
10Monitoring
In trials, extensively, by clinicians. Outside trials, not at all. Nobody is checking your glucose, kidney function or anything else, and there is no route to report harm through the Yellow Card scheme for an unlicensed product.
11Questions worth asking
Take these to a doctor or pharmacist. A good clinician will not mind being asked, and the answers are specific to you in a way nothing on this page can be.
- Is there a UK trial recruiting that I could join? (Be Part of Research lists them.)
- Given this is years from availability, what licensed option makes sense now?
12Common questions
Is retatrutide legal in the UK?
It has no marketing authorisation, so supplying it for human use is prohibited under the Human Medicines Regulations 2012. The only lawful route to receiving it is enrolment in an authorised clinical trial.
Why is it sold as research use only if it is a drug in trials?
Because that label places the seller outside medicines regulation. It describes their legal position, not the product's quality, and it does not survive scrutiny when the same site publishes dosing tables aimed at consumers.
Is it really the most effective one?
Phase 2 data suggested the largest weight reduction figures seen in the class, and phase 3 reporting has been striking. But it has not been through regulatory assessment, so nobody independent has yet judged whether the benefits outweigh the risks.
13Sources
Links go to the authoritative source. Where a document sits behind a paywall or moves around, the full citation is given so you can find it yourself.
- Be Part of Research trial finderNIHR
- TRIUMPH programme recordsClinicalTrials.gov
- Phase 2 retatrutide trialNew England Journal of Medicine, 2023
- Guidance on buying medicines onlineMHRA
- Unlicensed medicines guidanceMHRA
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