Retatrutide is a novel single-molecule tri-agonist targeting the GLP-1, GIP, and glucagon receptors simultaneously — a profile referred to as GLP-3R. GLP-1 receptor activation enhances insulin secretion and reduces appetite; GIP receptor activation improves insulin sensitivity and fat tissue metabolism; glucagon receptor activation increases energy expenditure and hepatic fat mobilization. The combination of all three mechanisms in one molecule represents a significant advancement over earlier dual or single-target incretin compounds, and retatrutide has demonstrated substantial metabolic and body composition effects in early-phase research.