Retatrutide
Published phase 2 trials in people. Phase 3 under way. Not approved anywhere.
At a glance. An experimental weekly compound that acts on three appetite and metabolism hormone receptors at once. Sold by AVERON as R3TA GLP3.
Written and maintained by the AVERON Research Desk · Last reviewed September 2026
What it is
Retatrutide is an investigational compound being developed by Eli Lilly under the code LY3437943. It is a single peptide that activates three hormone receptors at the same time: the receptors for GIP, GLP-1 and glucagon. That makes it what researchers call a triple agonist.
The first two receptors are the same ones targeted by tirzepatide. The third, the glucagon receptor, is the addition. Glucagon signalling increases energy expenditure and affects how the liver handles fat, which is why researchers expected a triple agonist to produce greater effects than a single or dual agonist.
What researchers study it for
Retatrutide is being studied mainly for obesity, and also for type 2 diabetes, fatty liver disease, and conditions linked to excess weight such as knee osteoarthritis.
What the research shows
The key published evidence is a phase 2 trial led by Ania Jastreboff and colleagues, published in the New England Journal of Medicine in 2023. It enrolled 338 adults with obesity, or overweight with at least one related condition, and without diabetes. Participants received retatrutide once weekly at one of several doses, or a placebo, for 48 weeks.
After 24 weeks, average weight change was −7.2% at 1 mg, −12.9% at 4 mg, −17.3% at 8 mg and −17.5% at 12 mg, compared with −1.6% on placebo.
After 48 weeks, average weight change was −8.7% at 1 mg, −17.1% at 4 mg, −22.8% at 8 mg and −24.2% at 12 mg, compared with −2.1% on placebo.
Those are among the largest reductions reported for any weight-management compound in a trial of this stage. A separate phase 2 trial has also been published in people with type 2 diabetes. A phase 3 programme, called TRIUMPH, is under way.
What it does not do, and what is not known
- It is not an approved medicine anywhere. No regulator has reviewed its full safety and efficacy data.
- Its long-term safety is not established. Phase 2 trials are too short and too small to detect rare or delayed effects.
- Its effect on heart attacks, strokes and survival has not been measured.
- Weight lost on this class of compound tends to return when it is stopped, based on experience with related drugs.
- Phase 2 results do not always hold up in larger phase 3 trials.
- Research-grade material is not the product being tested in Lilly's trials.
Adverse effects reported in research
In the phase 2 obesity trial, the most common adverse effects were gastrointestinal: nausea, diarrhoea, vomiting and constipation. They were mostly mild to moderate and were most frequent while the dose was being increased. Heart rate rose in a dose-related way, peaking at around 24 weeks and then declining. Discontinuation because of adverse effects was more common at higher doses.
Regulatory and anti-doping status
Regulatory: Investigational. Not approved by the US FDA, the European Medicines Agency or Indonesia's BPOM.
Anti-doping: Because it has no approval for human therapeutic use anywhere, retatrutide falls under WADA's category S0 (non-approved substances), which explicitly includes drugs under clinical development. It is prohibited at all times in tested sport.
At AVERON
Supplied as research-grade material under the name R3TA GLP3, in 10 mg and 20 mg vials.
Independent lab reports: 10 mg — 123380_6XL5H95NCLHB · 20 mg — 99341_RTX7IF6JUW83
Frequently asked questions
Doses mentioned on this page are the arms of published trials, given to describe their results. They are not guidance.