Retatrutide
Also known as: LY3437943
Educational content only. This page does not constitute medical advice, diagnosis, or treatment recommendations. Always consult a qualified healthcare professional before making decisions related to any medication or health intervention.
Overview
Retatrutide (LY3437943) is an investigational synthetic peptide developed by Eli Lilly. It is classified as a triple hormone receptor agonist, meaning it activates three receptors simultaneously: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor, and the glucagon receptor. This triple-agonist mechanism is a first-in-class approach, adding glucagon receptor activation to the dual GIP/GLP-1 mechanism seen in tirzepatide.
Retatrutide is designed to be administered as a once-weekly subcutaneous injection. The addition of the glucagon receptor target is hypothesized to contribute to additional energy expenditure and metabolic effects beyond what dual agonists achieve. As of early 2026, retatrutide remains an investigational compound and has not been approved for any indication by any regulatory authority.
Research & Clinical Context
Retatrutide has advanced through Phase 2 trials and is currently in Phase 3 development under the TRIUMPH clinical trial program. The Phase 2 trial, published in the New England Journal of Medicine in 2023, evaluated multiple doses in adults with obesity over 48 weeks and reported substantial dose-dependent reductions in body weight at the highest dose level studied.
The TRIUMPH program consists of four Phase 3 trials enrolling over 5,800 participants, evaluating retatrutide for obesity and overweight, obstructive sleep apnea in people with obesity, knee osteoarthritis in people with obesity, and cardiovascular and renal outcomes. The first Phase 3 readout (TRIUMPH-4) was announced in December 2025, with seven additional readouts expected in 2026. Eli Lilly has also initiated additional studies including head-to-head comparisons and maintenance dosing strategies.
References
- Jastreboff AM, et al. "Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial." NEJM (2023)
New England Journal of Medicine
- TRIUMPH-4 Trial
ClinicalTrials.gov
- ClinicalTrials.gov Search: Retatrutide
ClinicalTrials.gov
Safety & Regulatory Notes
Retatrutide is an investigational drug that has not been approved by the FDA or any other regulatory authority for any indication. It is currently available only through enrollment in clinical trials. The safety profile observed in Phase 2 and early Phase 3 data has been generally consistent with other incretin-class therapies, with gastrointestinal symptoms being the most commonly reported adverse events. However, the full safety profile will not be established until the Phase 3 program is complete.
As an investigational compound, retatrutide is not legally available through pharmacies, compounding services, or research chemical suppliers for human use. Regulations vary by country. Readers should consult a licensed healthcare provider for any decisions about investigational therapies or clinical trial participation.
How This Fits Into Our Peptide Hub
Retatrutide is the leading next-generation investigational peptide tracked on our platform. It appears in our pipeline tracker, is commonly compared with tirzepatide and semaglutide in our research summaries, and is a key molecule in the GLP-1 and metabolic peptide educational sections.