GLP-1 Receptor Agonists & Incretin Mimetics

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of peptides and small molecules that mimic the incretin hormone GLP-1, which is secreted by intestinal L-cells in response to nutrient ingestion. The class has evolved from first-generation GLP-1-only agonists (Liraglutide, Semaglutide) to dual and triple receptor agonists (Tirzepatide, Retatrutide) and now small molecule oral agonists (Orforglipron). These agents represent the fastest-growing therapeutic peptide class in clinical development.

Native GLP-1 (7-36) amide activates the GLP-1 receptor (GLP-1R), a class B GPCR, triggering Gs-mediated cAMP elevation in pancreatic beta-cells that drives glucose-dependent insulin secretion, suppresses alpha-cell glucagon release, slows gastric emptying, and activates hypothalamic satiety circuits to reduce appetite. Pharmaceutical analogs are engineered to resist DPP-4 cleavage (the enzyme that inactivates native GLP-1 in minutes). Tirzepatide adds GIP receptor co-agonism; Retatrutide adds both GIP and glucagon receptor activation.

Semaglutide (Ozempic/Wegovy) and Liraglutide (Victoza/Saxenda) are FDA-approved for type 2 diabetes and/or chronic weight management. Tirzepatide (Mounjaro/Zepbound) is approved for both indications. Retatrutide is in Phase 3 trials for obesity. Orforglipron completed a positive Phase 3 weight loss trial in 2025. Survodutide, Cagrilintide, and Mazdutide are in Phase 2–3 trials globally.

Key research variables for GLP-1 class agents include receptor selectivity ratios (GLP-1:GIP:glucagon), half-life and dosing interval, tolerability profiles (particularly nausea and GI adverse events), and efficacy endpoints (HbA1c reduction vs. percent body weight loss). The field is moving toward combination approaches (e.g., CagriSema = Cagrilintide + Semaglutide) that target multiple appetite pathways simultaneously.