Retatrutide (LY3437943)

Retatrutide is a novel triple agonist peptide that simultaneously activates three key metabolic receptors: glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon receptors. Developed by Eli Lilly, it represents the next generation of incretin-based therapeutics, building upon the dual-agonist approach of tirzepatide by adding glucagon receptor activation. The addition of glucagon receptor agonism distinguishes retatrutide from its predecessors. Glucagon activation increases energy expenditure and promotes hepatic lipid oxidation, potentially enhancing weight loss beyond what is achievable with GLP-1/GIP dual agonism alone. This tripartite mechanism addresses multiple metabolic pathways simultaneously.

Retatrutide's mechanism involves activation of three G protein-coupled receptors: **GLP-1 Receptor Activation:** Stimulates insulin secretion in a glucose-dependent manner, suppresses glucagon release, slows gastric emptying, and activates central satiety pathways in the hypothalamus, reducing appetite and food intake. **GIP Receptor Activation:** Enhances insulin secretion, improves insulin sensitivity in adipose tissue, and may provide direct effects on fat metabolism. GIP also appears to potentiate the effects of GLP-1 on appetite suppression. **Glucagon Receptor Activation:** Increases hepatic glucose production (counterbalanced by insulin effects), promotes lipolysis and fatty acid oxidation, increases energy expenditure, and stimulates hepatic amino acid metabolism. This thermogenic effect contributes to enhanced caloric expenditure. The combined activation creates a synergistic effect where the metabolic benefits of each pathway are amplified while individual side effects may be attenuated.