The constitutive androstane receptor (CAR) also known as nuclear receptor subfamily 1, group I, member 3 is a protein that in humans is encoded by the "NR1I3" gene. CAR is a member of the nuclear receptor superfamily and along with pregnane X receptor (PXR) functions as a sensor of and xenobiotic substances. In response, expression of proteins responsible for the metabolism and excretion of these substances is upregulated. Hence, CAR and PXR play a major role in the detoxification of foreign substances such as drugs.