GPR109A, also known as Nicotinic Acid Receptor 1 (NIACR1), is a member of the G protein-coupled receptor family with seven transmembrane domains. It is primarily expressed in adipocytes, immune cells, and intestinal cells, participating in the regulation of fatty acid metabolism, anti-inflammatory responses, and cholesterol metabolism. By activating Gi/o proteins, GPR109A inhibits cAMP generation while activating the ERK1/2 and β-arrestin pathways. It exhibits high affinity for nicotinic acid and β-hydroxybutyrate. Gene-specific expression occurs in some metabolism-related tissues, and mutations or changes in expression levels are associated with metabolic disorders and inflammatory conditions.