Retatrutide
Also known as: LY3437943, LY-3437943, RETA
5 notable studies · 6 references
TLDR
Retatrutide is an investigational GIP, GLP-1, and glucagon triple-receptor agonist with strong Phase 2 and Phase 3 human evidence for substantial weight reduction and metabolic improvement, but it remains unapproved while its long-term outcomes and regulatory review continue to develop.
At a Glance
Classification: Long-acting single-peptide triple agonist of the GIP, GLP-1, and glucagon receptors; investigational metabolic peptide
Retatrutide is an investigational peptide developed by Eli Lilly that activates three metabolic hormone receptors: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon. Researchers are studying this combination primarily for obesity, type 2 diabetes, and obesity-related conditions. Unlike many compounds discussed in research-peptide communities, retatrutide has an extensive human clinical-development program and has progressed through multiple Phase 3 trials. In the pivotal TRIUMPH-1 obesity trial, participants receiving the highest studied dose had an average estimated weight reduction of 28.3% at 80 weeks. In the recently published TRIUMPH-2 Phase 3 trial involving people with obesity or overweight and type 2 diabetes, average weight reduction reached 20.8% at 80 weeks. Despite these results, retatrutide remains an investigational drug as of October 2026 and has not been approved by FDA or another regulatory agency.
What Is Retatrutide?
Retatrutide is a synthetic long-acting peptide engineered to activate the receptors for GIP, GLP-1, and glucagon simultaneously. This distinguishes it from: - Semaglutide, which primarily activates the GLP-1 receptor - Tirzepatide, which activates GIP and GLP-1 receptors - Retatrutide, which adds glucagon-receptor agonism to GIP/GLP-1 activity The compound was engineered as a single peptide conjugated to a fatty-acid-related moiety that extends its duration of action. Early pharmacological work showed activity at all three receptors. Human pharmacokinetic studies found a half-life of approximately six days, supporting the once-weekly schedule used in clinical trials. The rationale for adding glucagon-receptor agonism is particularly interesting. GLP-1 and GIP signaling can influence appetite, food intake, insulin secretion, and metabolic regulation, while glucagon signaling may additionally influence energy expenditure, substrate metabolism, and other aspects of energy balance. The challenge is achieving a balance among the three receptor activities that produces useful metabolic effects without unacceptable adverse effects.
What Are Researchers Studying?
Type 2 diabetes and glycemic regulation
Retatrutide has been investigated in people with type 2 diabetes since early clinical development. A randomized Phase 2 trial demonstrated reductions in HbA1c and body weight, establishing the basis for larger clinical studies. The Phase 3 TRIUMPH-2 trial subsequently evaluated 1,152 adults with obesity or overweight and type 2 diabetes. At 80 weeks, participants receiving retatrutide experienced substantial weight reduction alongside improved glycemic control.
Knee osteoarthritis associated with obesity
Researchers have investigated whether substantial weight reduction with retatrutide affects pain and physical function in people with obesity and knee osteoarthritis. Phase 3 TRIUMPH-1 osteoarthritis data reported substantial reductions in body weight and WOMAC pain scores. These findings raise an important mechanistic question: how much improvement results from reduced mechanical loading associated with weight loss versus additional metabolic or inflammatory effects remains an area for further study.
Obstructive sleep apnea
Retatrutide has also been investigated in people with obesity and moderate-to-severe obstructive sleep apnea. Phase 3 results reported substantial reductions in apnea-hypopnea index alongside weight reduction. As with osteoarthritis, separating direct pharmacological effects from consequences of major weight reduction is an important consideration.
Cardiovascular and cardiometabolic risk
Clinical trials have measured blood pressure, waist circumference, lipid markers, glucose regulation, and other cardiometabolic outcomes. The Phase 2 obesity trial reported improvements across several cardiometabolic measures accompanying weight reduction. Phase 3 TRIUMPH-3 specifically studied adults with severe obesity and established cardiovascular disease, with or without type 2 diabetes, and reported substantial weight reduction. Longer-term research is needed to determine the effect of retatrutide on cardiovascular events and outcomes.
How Does It Work?
Retatrutide activates three G-protein-coupled hormone receptors: GLP-1 receptor activation influences appetite, food intake, glucose-dependent insulin secretion, gastric physiology, and glycemic regulation. GIP receptor activation influences glucose-dependent insulin secretion and participates in nutrient and adipose-tissue signaling. Glucagon receptor activation affects hepatic metabolism, substrate utilization, glucose regulation, and energy expenditure. The therapeutic hypothesis behind retatrutide is that carefully combining these three signaling systems can produce greater effects on energy balance and metabolic regulation than targeting one or two receptors alone. Retatrutide does not activate all three receptors equally. Early pharmacological characterization found different relative activity at each receptor compared with their endogenous ligands, suggesting that the compound was deliberately engineered around a particular balance of receptor activity.
What Does the Research Show?
Human research
Retatrutide has a substantial human evidence base for an investigational compound. Phase 1 studies established early pharmacokinetic and safety information. Two major Phase 2 trials published in 2023 investigated obesity and type 2 diabetes. The obesity trial demonstrated dose-dependent weight reduction, reaching an average 24.2% at 48 weeks with the highest studied dose. Gastrointestinal events were the most common adverse events and were generally mild to moderate. Dose-dependent increases in heart rate were observed, peaking around week 24 before declining. The development program then progressed to Phase 3. TRIUMPH-1 reported average estimated weight reductions of: - 19.0% with 4 mg - 25.9% with 9 mg - 28.3% with 12 mg at 80 weeks in adults with obesity or overweight without diabetes. TRIUMPH-2 enrolled 1,152 participants with obesity or overweight and type 2 diabetes. At 80 weeks, average weight reductions were approximately: - 12.7% with 4 mg - 19.1% with 9 mg - 20.8% with 12 mg versus approximately 4.0% with placebo. Retatrutide therefore has considerably stronger human evidence than many compounds listed on Aminodex, but its regulatory evaluation is not complete.
Animal research
Preclinical research was central to designing retatrutide and determining whether simultaneous GIP, GLP-1, and glucagon receptor agonism could produce useful metabolic effects. Animal experiments evaluated food intake, energy expenditure, body weight, glucose regulation, and lipid metabolism. These studies helped establish the pharmacological rationale for moving retatrutide into human development. Now that substantial randomized human evidence exists, animal data are more useful for understanding mechanisms than for estimating clinical efficacy.
In-vitro research
Cellular and receptor-based experiments have characterized retatrutide's activity at human GIP, GLP-1, and glucagon receptors. These studies demonstrate that retatrutide has deliberately unequal potency across the three receptors and help researchers investigate how its receptor balance differs from endogenous hormones and other incretin-based compounds. In-vitro receptor activity establishes pharmacological mechanism but cannot independently predict clinical outcomes.
Notable Studies
LY3437943, a Novel Triple GIP, GLP-1, and Glucagon Receptor Agonist in People With Type 2 Diabetes: A Phase 1b, Multicentre, Double-Blind, Placebo-Controlled, Randomised, Multiple-Ascending Dose Trial
humanResearchers investigated the safety, pharmacokinetics, pharmacodynamics, glucose effects, and body-weight effects of LY3437943, later named retatrutide, in people with type 2 diabetes. The study provided early human evidence supporting once-weekly administration and demonstrated reductions in glucose and body weight sufficient to support further clinical development.
Limitations: This was an early-phase, relatively short study designed primarily to characterize initial human pharmacology rather than establish long-term clinical effectiveness or safety.
View publication →Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial
humanResearchers randomized adults with obesity or overweight plus a weight-related condition to several retatrutide regimens or placebo for 48 weeks. Weight reduction was strongly dose dependent. At 48 weeks, average weight reduction reached 24.2% in the 12-mg group. At that dose, 100% of participants included in the reported threshold analysis lost at least 5% of body weight, 93% lost at least 10%, and 83% lost at least 15%. Weight-loss curves had not clearly plateaued by week 48.
Limitations: The study lasted 48 weeks and was not designed to establish long-term cardiovascular outcomes or uncommon safety events. It was funded by Eli Lilly, the developer of retatrutide. Longer and larger Phase 3 trials were necessary to characterize efficacy and safety more completely.
View publication →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
humanResearchers investigated retatrutide in adults with type 2 diabetes. The study compared multiple retatrutide regimens with placebo and an active comparator and examined HbA1c, body weight, safety, and tolerability. Retatrutide produced clinically meaningful reductions in HbA1c and body weight, supporting continued development for people with type 2 diabetes and obesity.
Limitations: The study was Phase 2 and therefore smaller and shorter than subsequent pivotal trials. Long-term safety and cardiovascular outcomes could not be established.
View publication →The First Phase 3 Obesity Study of Retatrutide, a GIP, GLP-1, and Glucagon Receptor Agonist, in People With Obesity (TRIUMPH-1)
humanTRIUMPH-1 evaluated retatrutide in adults with obesity or overweight without diabetes. At 80 weeks, estimated average body-weight reductions reached 19.0%, 25.9%, and 28.3% with 4 mg, 9 mg, and 12 mg respectively, compared with approximately 2.2% with placebo. In a study extension involving participants with a baseline BMI of at least 35, average weight reduction reached approximately 30.3% at 104 weeks at the highest dose.
Limitations: As of this profile update, detailed peer-reviewed publication of all TRIUMPH-1 results should be distinguished from company-reported Phase 3 results and scientific-meeting presentations. The trial was sponsored by the drug's manufacturer. Weight reduction itself does not establish effects on long-term cardiovascular morbidity or mortality.
View publication →Retatrutide in Adults With Obesity and Type 2 Diabetes (TRIUMPH-2): A Double-Blind, Parallel-Group, Randomised, Placebo-Controlled, Phase 3 Trial
humanTRIUMPH-2 enrolled 1,152 adults with obesity or overweight and type 2 diabetes across 92 centers in eight countries. Researchers evaluated three retatrutide doses against placebo over 80 weeks. Average body-weight reduction reached 20.8% with 12 mg, alongside substantial improvement in glycemic control. This represents pivotal Phase 3 evidence and substantially strengthens the human evidence base compared with the earlier Phase 2 program.
Limitations: The study population specifically had type 2 diabetes plus obesity or overweight, so results should not automatically be generalized to all populations. The trial was sponsored by Eli Lilly, and several authors were company employees. Longer-term follow-up remains important for uncommon adverse events and clinical cardiovascular outcomes.
View publication →What We Still Don't Know
Despite the unusually strong clinical evidence for an investigational compound, important questions remain: - Final regulatory assessment of retatrutide - Long-term safety beyond the clinical-trial durations studied - Effects on major cardiovascular events and mortality - Durability of weight reduction during prolonged treatment - Outcomes after discontinuation - Long-term effects of sustained glucagon-receptor agonism - Which patients benefit most from triple-receptor agonism - Whether the magnitude of weight reduction translates into proportionally greater improvements in long-term health outcomes - The relative contribution of GIP, GLP-1, and glucagon signaling to different clinical effects - Long-term effects on body composition, including lean mass - How retatrutide will compare directly with other next-generation obesity therapies in adequately powered head-to-head trials Regulatory status is particularly important: retatrutide is not currently an FDA-approved medication. Lilly currently says it plans to submit its application to FDA in the first quarter of 2027.
Related Compounds
Recent publications
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Sources & References
- Urva S, Coskun T, Loh MT, et al. LY3437943, a Novel Triple GIP, GLP-1, and Glucagon Receptor Agonist in People With Type 2 Diabetes: A Phase 1b, Multicentre, Double-Blind, Placebo-Controlled, Randomised, Multiple-Ascending Dose Trial. The Lancet. 2022.
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. 2023;389(6):514–526. doi:10.1056/NEJMoa2301972.
- Rosenstock J, Frias J, Jastreboff AM, et al. 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. 2023;402(10401):529–544. doi:10.1016/S0140-6736(23)01053-X.
- Jastreboff AM, et al. The First Phase 3 Obesity Study of Retatrutide, a GIP, GLP-1, and Glucagon Receptor Agonist, in People With Obesity (TRIUMPH-1). Presented at the American Diabetes Association Scientific Sessions. 2026.
- Bellido V, le Roux CW, Ekinci EI, et al. Retatrutide in Adults With Obesity and Type 2 Diabetes (TRIUMPH-2): A Double-Blind, Parallel-Group, Randomised, Placebo-Controlled, Phase 3 Trial. The Lancet. 2026. doi:10.1016/S0140-6736(26)01861-1.
- Eli Lilly and Company. Retatrutide Phase 3 TRIUMPH Program Results. 2026.
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