Non-CYPs play an important role in the metabolism of many drugs. Non-CYP enzymes including carboxylesterase (CES), aldehyde oxidase (AO), monoamine oxidase (MAO), flavin monooxygenase (FMO), alcohol/aldehyde dehydrogenase (ADH/ALDH), xanthine oxidase (XO), UDP glucuronosyl transferases (UGT) and sulfotransferases (SULTs).