Fibroblast Growth Factor 19 (FGF19) is a hormone belonging to the FGF family, encoded by the FGF19 gene. It is primarily synthesized and secreted in the ileum in response to bile acid absorption, acting as a ligand for the farnesoid X receptor (FXR). FGF19's core function is to exert negative feedback on hepatic bile acid synthesis by binding to the Fibroblast Growth Factor Receptor 4 (FGFR4)/Klotho-β complex in the liver, thereby inhibiting cholesterol 7α-hydroxylase (CYP7A1). Additionally, it plays a role in glucose and lipid metabolism. Its mouse ortholog is FGF15, and they are often referred to collectively as FGF15/19. Altered FGF19 levels are implicated in chronic bile acid diarrhea and certain metabolic disorders.