 Methadone is metabolized by CYP3A4, CYP2B6, CYP2D6, and is a substrate, or in this case target, for the P-glycoprotein efflux protein, a protein which helps pump foreign substances out of cells, in the intestines and brain.The bioavailability and elimination half-life of methadone are subject to substantial interindividual variability.Its main route of administration is oral.