Oral Small-Molecule GLP-1 Receptor Agonists: Mechanistic Insights and Emerging Therapeutic Strategies

Small-molecule glucagon-like peptide-1 receptor agonists (GLP-1RAs) represent an innovative advancement in oral therapeutics, addressing key limitations associated with injectable peptide-based incretin therapies. These nonpeptidic agents exert their actions primarily through non-canonical binding orthosteric sites within the GLP-1 receptor transmembrane domain, enabling selective G protein (Gs)-biased signaling with reduced β-arrestin-mediated adverse effects. Orforglipron has notably advanced through Phase 3 clinical development, demonstrating significant reductions in hemoglobin A1c and body weight (up to 7.9%) with favorable tolerability. Conversely, promising candidates such as danuglipron and lotiglipron were discontinued due to hepatotoxicity, underscoring critical safety concerns intrinsic to small-molecule GLP-1RA development. Current clinical candidates, including GSBR-1290, CT-996, and ECC5004, continue to offer substantial potential due to their oral bioavailability, simplified dosing regimens, and favorable gastrointestinal tolerability. Nevertheless, challenges persist regarding hepatic safety, pharmacodynamic variability, and limited long-term outcome data. This review integrates current structural, pharmacological, and clinical evidence, highlights key mechanistic innovations—including biased agonism, covalent binding strategies, and allosteric modulation—and discusses future directions for this rapidly evolving therapeutic class in metabolic disease management.