What it is

Retatrutide is an investigational peptide from Eli Lilly that activates three hormone receptors at once: GIP, GLP-1 and glucagon. Because it adds glucagon-receptor activity to the GIP/GLP-1 combination used by tirzepatide, it is often called a triple agonist. A fatty-acid side chain lets it bind albumin in the blood, which stretches its half-life to roughly six days and supports once-weekly dosing in trials.

How it works

GLP-1 and GIP receptor activation slows gastric emptying, increases glucose-dependent insulin release and acts on appetite centers in the brain. Glucagon-receptor activation raises energy expenditure and promotes fat oxidation in the liver. The combination is designed to add an energy-expenditure effect on top of the appetite effect of earlier incretin drugs.

What the research shows

Phase 2 obesity trial (Jastreboff et al., New England Journal of Medicine, 2023): the highest dose produced a mean weight reduction of about 24% at 48 weeks.
Phase 3 TRIUMPH program (reported 2025 to 2026): Lilly reported mean weight loss of 28.3% at 80 weeks on the 12 mg dose in TRIUMPH-1, 20.8% in adults with type 2 diabetes (TRIUMPH-2) and 22.6% in adults with obesity and cardiovascular disease (TRIUMPH-3).
Reported side effects in trials are mostly gastrointestinal (nausea, diarrhea, vomiting), similar to other incretin drugs, plus a dose-related rise in heart rate.

Regulatory status

Retatrutide is not FDA-approved. As of mid-2026, Lilly said it planned to file for FDA approval in early 2027. Material sold as "research retatrutide" is not the Lilly drug product and has not been evaluated for quality or safety.

Storage and handling

Lyophilized (freeze-dried) powder is most stable sealed, dry and protected from light. Laboratory practice is to keep unopened vials frozen at about -20 °C for long-term storage, or refrigerated at 2 to 8 °C for shorter periods. After reconstitution, keep the solution refrigerated at 2 to 8 °C, avoid repeated freeze-thaw cycles and use aseptic technique for every draw. Formal stability data in solution has not been published for most research peptides, so follow the supplier's label and certificate of analysis.

Reconstitution math

To work out concentration, volume and U-100 syringe units for any vial size, use the reconstitution calculator with Retatrutide selected. Always confirm the vial content against the label and the batch's certificate of analysis.

Key references

Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023.
Eli Lilly TRIUMPH phase 3 announcements, December 2025 to July 2026.
Search PubMed for Retatrutide studies

Educational content only

Peptide Knowledge is an educational reference. Nothing on this site is medical advice, a treatment recommendation or dosing guidance. Many compounds described here are not approved for human use and are sold for laboratory research only. Talk to a licensed clinician before starting, stopping or changing any medication or supplement.

Retatrutide