The CAR (Constitutive Androstane Receptor) is a receptor located within the cell nucleus, belonging to the nuclear receptor superfamily. It is activated by sensing exogenous and endogenous compounds, involved in regulating the gene expression of drug metabolism, lipid metabolism, and energy balance. CAR is primarily expressed in liver cells but can also be found in other tissues such as the kidneys and small intestine. By binding to specific ligands, CAR activates the expression of genes associated with drug-metabolizing enzymes and transport proteins, affecting the processing of xenobiotics in the body. Genetic variations that affect CAR's activity or expression can lead to increased or decreased sensitivity to certain drugs, affecting drug efficacy and toxicity.