Retatrutide

What Is Retatrutide?

Retatrutide is an investigational synthetic peptide that activates three hormone receptors at once: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor and the glucagon receptor.^[1] It was discovered by Eli Lilly and Company under the development code LY3437943, and the company has sponsored its clinical trials.^[1][2]

The compound belongs to a newer generation of incretin-based molecules. GLP-1 receptor agonists such as semaglutide were followed by the GIP/GLP-1 co-agonist tirzepatide, and retatrutide adds glucagon-receptor activity to that combination.^[3][4] For this reason it is usually described in the literature as a triple agonist or triple hormone receptor agonist.

Retatrutide is studied mainly as a candidate therapy for obesity and type 2 diabetes. Its phase 3 program also includes obesity-related complications, specifically obstructive sleep apnea and knee osteoarthritis.^[5]

Chemical Structure and Molecular Identity

Retatrutide is a 39-residue linear peptide with a fatty-acid side chain. PubChem (CID 171390338) records the free peptide as C221H342N46O68 with a molecular weight of 4731 g/mol, and its CAS Registry Number is 2381089-83-2.

Structural features

• Non-coded residues: the PubChem structure contains two α-aminoisobutyric acid (Aib) residues, at positions 2 and 20, and an α-methyl-L-leucine at position 13.
• Lipidation: the side chain of lysine 17 is acylated with a C20 fatty diacid (eicosanedioic acid) attached through a γ-glutamic acid and an 8-amino-3,6-dioxaoctanoic acid linker.
• Termini: a free N-terminal tyrosine and an amidated C-terminal serine.

Because of the Aib and α-methyl residues, the sequence cannot be written fully in the standard one-letter amino-acid code. PubChem also lists the informal synonym “Triple G”.

A note on mass values: figures near 4845 that appear in some sources correspond to a trifluoroacetate (TFA) salt form, not the free peptide described in the PubChem record.

Research History and Development

Retatrutide’s published record runs from a 2022 discovery and proof-of-concept report, through phase 2 trials published in 2023 and 2024, to phase 3 results in 2026.

Discovery and first-in-human study

The 2022 discovery paper described LY3437943 in cell-based assays, in obese mice and in a phase 1 single ascending dose study. In that study the compound showed a safety and tolerability profile similar to other incretins, and body-weight reduction persisted up to day 43 after a single dose.^[1]

Phase 2

A 48-week, double-blind, placebo-controlled phase 2 trial enrolled 338 adults with obesity, or with overweight plus at least one weight-related condition, and compared several dose levels.^[2] A substudy of 98 participants from that trial who had metabolic dysfunction-associated steatotic liver disease (MASLD) and at least 10% liver fat examined changes in liver fat.^[6]

Phase 3

The TRIUMPH program consists of four phase 3 trials in more than 5,800 participants, using a basket design that nests sleep apnea and knee osteoarthritis protocols within weight-management trials and includes one trial in people with cardiovascular disease.^[5] Separately, TRANSCEND-T2D-1 tested retatrutide as monotherapy in 537 adults with type 2 diabetes, and TRIUMPH-2 enrolled 1,152 adults with obesity and type 2 diabetes across eight countries.^[7][8]

Mechanisms Studied in Research

Retatrutide is studied as one molecule that combines incretin-driven reductions in food intake with glucagon-driven increases in energy expenditure. Most mechanistic data come from cell assays and rodent models, with supporting measurements from human trials.

Receptor activity in vitro

In cell-based assays, LY3437943 showed balanced activity at the glucagon receptor (GCGR) and GLP-1 receptor (GLP-1R) but greater activity at the GIP receptor (GIPR).^[1]

Animal models

In obese mice, the compound decreased body weight and improved glycemic control. The authors attributed the added weight loss to GCGR-mediated increases in energy expenditure layered on top of GIPR- and GLP-1R-driven reductions in calorie intake.^[1] A 2025 review of preclinical work reports that animal studies also show delayed gastric emptying and reduced food intake.^[9]

In db/db mice, a model of type 2 diabetes with kidney disease, retatrutide suppressed renal expression of pro-inflammatory markers (TNF-α, caspase-1, NLRP3) and pro-fibrotic factors (fibronectin, α-SMA, collagen I), and increased levels of the intestinal metabolite butyrate.^[10]

Human metabolic measures

In the phase 2a MASLD substudy, reductions in liver fat were significantly related to changes in body weight, abdominal fat, and metabolic measures associated with improved insulin sensitivity and lipid metabolism.^[6]

Key Findings From Published Studies

Across phase 2 and phase 3 trials, retatrutide produced dose-dependent reductions in body weight and glycated hemoglobin (HbA1c) compared with placebo, and gastrointestinal events were the most common adverse effects.^[2][7][8]

Obesity

In the phase 2 trial in adults with obesity, 83% of participants in the highest-dose arm lost 15% or more of body weight by 48 weeks, compared with 2% on placebo.^[2] A 2025 systematic review of placebo-controlled trials in adults without diabetes found that retatrutide’s highest-dose arm produced placebo-adjusted weight loss of up to 22.1% at 48 weeks, though no head-to-head trials against other agents were available.^[11] A meta-analysis of three randomized trials (878 patients) reported a mean body-weight difference of −14.33% versus placebo, along with lower waist circumference, HbA1c and blood pressure, and no significant difference in overall adverse events.^[12]

Type 2 diabetes and liver fat

In TRANSCEND-T2D-1, no severe hypoglycemia was reported, and discontinuations due to adverse events were 2–5% with retatrutide versus 0% with placebo.^[7] In TRIUMPH-2, the estimated treatment difference in body weight versus placebo was −13.8% in the highest-dose arm.^[8] In the MASLD substudy, 86% of the highest-dose arm reached normal liver fat (below 5%) at 24 weeks, compared with none on placebo.^[6]

Safety signals and animal data

In phase 2, gastrointestinal adverse events were dose-related and mostly mild to moderate, and dose-dependent heart-rate increases peaked at 24 weeks and declined afterward.^[2] A review of incretin-based agents, including retatrutide, notes that this drug class can cause substantial loss of lean mass alongside fat loss.^[13] In db/db mice, retatrutide outperformed liraglutide and tirzepatide on body weight and kidney-function measures, but not on blood-glucose lowering.^[10]

For a long, lipidated peptide like retatrutide, batch-specific HPLC and mass spectrometry certificates of analysis are the practical way to confirm identity and purity.

Regulatory and Research Status

Retatrutide is an investigational compound. The 2026 phase 3 reports describe it as under clinical development for obesity, type 2 diabetes and related complications, and it was not an FDA-approved medicine when those studies were published.^[7][8]

The TRIUMPH trials are evaluating weight management, obstructive sleep apnea and knee osteoarthritis outcomes, including a trial in a population with cardiovascular disease.^[5] Reviews of the obesity pipeline place retatrutide among the phase 3 candidates alongside the GLP-1/glucagon co-agonists survodutide and mazdutide and a cagrilintide–semaglutide combination.^[14][4]

Reviewers identify several open questions: long-term safety, maintenance of weight loss, effects on mortality and cardio-renal outcomes, and the composition of weight lost.^[14][15][9] Outside registered clinical trials, retatrutide is not approved for human use, and material described as retatrutide is intended for laboratory research only.