Overview
Retatrutide, also known by its development code LY3437943 and CAS number 2381089-83-2, is a synthetic 39-amino acid peptide developed by Eli Lilly and Company. It is the first unimolecular compound to simultaneously activate three key metabolic receptors: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon (GCG).
This triple-agonist mechanism distinguishes Retatrutide from all existing incretin-based compounds. Semaglutide activates only GLP-1. Tirzepatide activates GLP-1 and GIP. Retatrutide activates all three, producing compounding metabolic effects that no mono- or dual-agonist can replicate.
Molecular Structure
Retatrutide's peptide backbone is derived from the GIP sequence, with targeted amino acid substitutions that introduce GLP-1 and Glucagon receptor affinity. The molecule is modified with a C20 fatty diacid moiety that non-covalently binds serum albumin, protecting the peptide from enzymatic degradation by DPP-4 and extending its biological half-life to approximately 6 days.
Key structural specifications include a molecular formula of C₂₂₁H₃₄₂N₄₆O₆₈, a molecular weight of 4,731 g/mol, and a potency hierarchy tuned to be highest at the GIP receptor, moderate at GLP-1, and carefully calibrated at Glucagon to avoid hyperglycemic effects.
Triple-Receptor Mechanism
GLP-1 Receptor Activation
GLP-1 agonism suppresses appetite through central satiety signaling, slows gastric emptying to prolong nutrient absorption, and enhances glucose-dependent insulin secretion from pancreatic beta cells. This is the same pathway leveraged by semaglutide (Wegovy/Ozempic) — but in Retatrutide, the GLP-1 signal is amplified by concurrent GIP activation.
GIP Receptor Activation
GIP receptor activation enhances lipid metabolism in adipose tissue, improves insulin sensitivity, and buffers lipid handling during weight loss. In dual-agonist research with tirzepatide, GIP co-activation was shown to amplify the weight-loss effect of GLP-1 beyond what GLP-1 achieves alone. Retatrutide maintains this synergy while adding a third receptor.
Glucagon Receptor Activation
The Glucagon receptor is the key differentiator. GCG activation drives lipolysis in adipose tissue, increases resting energy expenditure through hepatic and brown-adipose-tissue thermogenesis, and has demonstrated a remarkable capacity for hepatic defatting. In Phase 2 substudies, GCG-mediated effects achieved greater than 86% reduction in liver fat content, with over 90% of MASLD subjects reaching normal liver fat levels below 5%.
Clinical Development Status
As of mid-2026, Retatrutide is in active Phase 3 clinical development across two major trial programs. The TRIUMPH series evaluates the compound in obesity and weight-related conditions. The TRANSCEND series evaluates its use in type 2 diabetes. TRIUMPH-4, reported in 2025, demonstrated 28.7% mean body weight reduction at the 12mg dose — the highest figure recorded for any single metabolic compound in a Phase 3 trial.
Research Applications
Retatrutide is currently sold as a research compound for in vitro and laboratory use only. It is not approved by the FDA or EMA for therapeutic use in humans. Research applications include metabolic pathway modeling, receptor binding studies, comparative agonist profiling, and pharmacokinetic analysis of acylated peptide stability.
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