Retatrutide is a synthetic peptide that activates three hormone receptors at the same time: the receptors for GIP, GLP-1 and glucagon. The company Eli Lilly developed it under the code LY3437943. As of 25 October 2026, retatrutide is in phase 3 clinical trials and is not an approved medicine in the EU or the US. This overview explains what the retatrutide peptide is, how it is built, how it acts at its three receptors, what the published studies investigated and why research suppliers sell it only for laboratory use.
What retatrutide is: a triple receptor agonist
An agonist is a molecule that binds to a receptor and activates it. Retatrutide is a triple agonist, because it activates three different receptors with a single molecule. All three receptors belong to the same family. They bind hormones that regulate blood sugar and energy balance:
GIP receptor: binds glucose-dependent insulinotropic polypeptide, a hormone from the upper small intestine.
GLP-1 receptor: binds glucagon-like peptide-1, a hormone from the lower small intestine and the colon.
Glucagon receptor: binds glucagon, a hormone from the pancreas.
GIP and GLP-1 are called incretins. The gut releases them after a meal. In online discussions, retatrutide is sometimes called "GLP-3" or "GLP-3RT", and the short form "reta peptide" is also common. These names are informal. There is no hormone called GLP-3. The terms only express that retatrutide addresses one more receptor than the dual agonist tirzepatide.
Retatrutide structure: a modified peptide chain
Retatrutide is a single peptide chain. Coskun and colleagues described its discovery in 2022 in Cell Metabolism. The sequence is a modified incretin-like chain that is designed to bind all three receptors. The chain contains non-standard amino acids that protect it against fast breakdown by enzymes. A fatty acid side chain is attached to the peptide. This side chain binds to albumin, a protein in the blood, and this extends the half-life of the molecule.
The same design principle, a modified peptide with a fatty acid side chain, is also used in semaglutide and tirzepatide. If you want to know more about how amino acids form a chain and why small changes in the sequence matter, our guide What are peptides? explains the basics.
How retatrutide acts at three receptors: the mechanism in plain words
Each of the three receptors starts a different signal in the cell. Researchers study retatrutide because it combines these signals in one molecule:
GLP-1 receptor: in research models, activation increases insulin release when blood sugar is high, slows gastric emptying and acts on appetite centres in the brain.
GIP receptor: activation also increases glucose-dependent insulin release. GIP signalling is also studied in fat tissue.
Glucagon receptor: activation acts mainly in the liver. It is studied for its role in energy expenditure and in the metabolism of liver fat.
The balance between the three signals is important. In cell assays, Coskun and colleagues reported balanced activity at the glucagon and GLP-1 receptors and higher activity at the GIP receptor. Researchers use such potency profiles to compare compounds in receptor pharmacology studies.
Retatrutide in clinical research: from phase 1 to phase 3
Medicines are tested in clinical trials in several phases. Phase 1 trials test safety and the behaviour of a compound in the body in a small group. Phase 2 trials examine different amounts in a larger group. Phase 3 trials compare the compound with placebo or a standard medicine in large groups. The published research on retatrutide covers all three phases:
Phase 1 (2022): Coskun and colleagues published the preclinical discovery data together with a first phase 1 study in humans.
Phase 2 in obesity (2023): Jastreboff and colleagues published a randomised, placebo-controlled trial with 338 adults over 48 weeks in the New England Journal of Medicine. The primary endpoint was the percentage change in body weight after 24 weeks compared with placebo.
Phase 2 in type 2 diabetes (2023): Rosenstock and colleagues published a trial with 281 participants in The Lancet. The primary endpoint was the change in HbA1c, a long-term blood sugar value, after 24 weeks.
Phase 3 (TRIUMPH programme): In 2026, Eli Lilly announced topline results from several phase 3 trials. In a press release of 23 July 2026, the company stated that it plans to submit retatrutide to the US Food and Drug Administration (FDA) in the first quarter of 2027.
The full results with all endpoints are in the original publications listed in the sources below. Topline results from a press release have not yet passed peer review.
Retatrutide is investigational, not an approved medicine
An investigational compound is a substance that is still tested in clinical trials. As of 25 October 2026, retatrutide has no marketing authorisation from the European Medicines Agency or the FDA. In clinical trials, it is given only to enrolled participants under medical supervision and under a trial protocol.
The retatrutide that research suppliers offer is a research chemical. It is made by peptide synthesis for laboratory work, for example for receptor pharmacology or for analytical reference. It is not the investigational product of the clinical trials and not a medicine. For this reason, peptidebio supplies retatrutide strictly for laboratory research and gives no dosing or medical advice.
Retatrutide compared with tirzepatide and semaglutide
Retatrutide belongs to a series of incretin-based peptides that differ mainly in the number of receptors they activate. The table compares the three compounds by receptor targets and by development status. It does not compare effects.
| Compound | Receptor targets | Type | Status as of 25 October 2026 |
|---|---|---|---|
| Semaglutide | GLP-1 | Single (mono) agonist | Approved as a prescription medicine in the EU |
| Tirzepatide | GLP-1, GIP | Dual agonist | Approved as a prescription medicine in the EU |
| Retatrutide | GLP-1, GIP, glucagon | Triple agonist | Investigational, phase 3 clinical trials |
All three compounds are available at peptidebio as lyophilised research peptides for laboratory use. They are listed together in the GLP-1 and metabolic peptides collection. The approval status in the table refers to the medicines of the manufacturers, not to research chemicals.
Storage and quality documentation of retatrutide
To buy retatrutide for laboratory research: we supply it as lyophilised powder in sealed glass vials of 5 mg, 10 mg and 15 mg, with a certificate of analysis on file. The certificate reports identity by mass spectrometry and purity by HPLC for the documented batch. Our guide mass spectrometry vs HPLC explains what each of the two tests shows.
Keep sealed vials at -20 °C for long-term storage, or at 2 to 8 °C for a few weeks, dry and away from light. After reconstitution with bacteriostatic water, keep the solution at 2 to 8 °C and use it within a short period. All orders ship from our warehouse in the Netherlands and arrive across Europe in 1 to 3 working days.
Frequently asked questions about retatrutide
Who developed retatrutide?
Retatrutide was developed by the pharmaceutical company Eli Lilly under the code LY3437943. The company also runs the clinical trial programme.
Is "reta peptide" the same compound as retatrutide?
Yes. "Reta" is an informal short form of retatrutide. The same applies to "GLP-3" or "GLP-3RT". The international non-proprietary name is retatrutide.
What is the difference between a dual and a triple agonist?
A dual agonist such as tirzepatide activates two receptors, GLP-1 and GIP. A triple agonist such as retatrutide also activates the glucagon receptor. Both are single molecules.
Where can I find registered retatrutide trials?
Clinical trials of retatrutide are registered in public registries such as ClinicalTrials.gov. A search for "retatrutide" or "LY3437943" lists the registered studies with their status.
Sources on retatrutide
Coskun T, Urva S, Roell WC, et al. (2022). LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metabolism 34(9):1234–1247. PubMed 35985340
Jastreboff AM, Kaplan LM, Frías JP, et al. (2023). Triple-Hormone-Receptor Agonist Retatrutide for Obesity – A Phase 2 Trial. New England Journal of Medicine 389(6):514–526. PubMed 37366315
Rosenstock J, Frias J, Jastreboff AM, et al. (2023). Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. The Lancet 402(10401):529–544. PubMed 37385280
Eli Lilly and Company (23 July 2026). Press release on the TRIUMPH-2 and TRIUMPH-3 phase 3 trials of retatrutide. investor.lilly.com
For laboratory research use only. Not for human or veterinary use. Not a medicine, supplement, food or cosmetic. This overview summarises published research and is not dosing or medical advice.