Retatrutide Guide

Retatrutide, also known as LY3437943, is an investigational once-weekly triple hormone receptor agonist being developed by Eli Lilly. It is called a triple agonist because one molecule is designed to activate the GIP, GLP-1, and glucagon receptors. [1]

The clearest way to think about retatrutide is not as a finished consumer product, but as a clinical-trial medicine candidate. Published Phase 2 work and later Lilly topline announcements have focused on obesity, type 2 diabetes, knee osteoarthritis in adults with obesity, and broader cardiometabolic conditions. [1][2][4][5]

Retatrutide combines activity at three metabolic hormone receptors. GLP-1 receptor activation is associated with appetite and glucose-regulation effects. GIP receptor activation is part of incretin signaling. Glucagon receptor activation is being studied because it may affect energy expenditure and liver metabolism, though the clinical tradeoffs still need careful evaluation. [1][2][3]

You may see retatrutide described online as “GLP-3.” That label is not a scientific drug class. Lilly describes the more accurate term as triple hormone receptor agonist or triple agonist. [1]

In the 2023 Phase 2 obesity trial published in the New England Journal of Medicine, adults with obesity or overweight and a weight-related condition received retatrutide or placebo for 48 weeks. The highest studied group had a mean body-weight reduction of 24.2% at 48 weeks, compared with 2.1% with placebo. [2]

In a Phase 2 type 2 diabetes trial published in The Lancet, retatrutide was studied against placebo and dulaglutide. The trial reported dose-dependent reductions in HbA1c and body weight over 36 weeks, supporting further study in type 2 diabetes populations. [3]

In March 2026, Lilly announced Phase 3 TRANSCEND-T2D-1 topline results in adults with type 2 diabetes. Lilly reported average A1C reductions of up to 2.0% and body-weight reduction up to 16.8% at 40 weeks with the efficacy estimand; detailed peer-reviewed publication was still pending in that announcement. [4]

In December 2025, Lilly announced TRIUMPH-4 topline results in adults with obesity or overweight and knee osteoarthritis. Lilly reported substantial weight loss and improvement in WOMAC pain and physical-function measures at 68 weeks. Because these were topline company results, they should be interpreted differently from peer-reviewed full trial publications. [5]

The most commonly reported adverse events in the Phase 2 obesity trial were gastrointestinal and dose-related. The paper also reported dose-dependent heart-rate increases that peaked around 24 weeks and declined afterward. [2]

In Lilly’s March 2026 TRANSCEND-T2D-1 announcement, common adverse events included nausea, diarrhea, and vomiting, mostly during dose escalation. Lilly also reported mild dysesthesia events in a minority of participants. [4]

The key point for readers: safety and efficacy are still being evaluated. Products sold as retatrutide outside clinical trials are not equivalent to regulated medicine and may have unknown identity, purity, strength, or contaminants. [1]

There is no approved public retatrutide product label, so there is no consumer storage standard to cite. Storage and handling for clinical-trial material belong to the trial protocol and study team, not public peptide-market assumptions. [1][6]

For approved medicines, storage instructions come from official labeling. Retatrutide does not currently have that kind of public prescribing label, so any seller-provided storage directions should not be treated as evidence of legitimacy. [1]