The primary objective of drug metabolism is to facilitate a drug’s excretion by increasing its hydrophilicity. The involved chemical modifications incidentally decrease or increase a drug’s pharmacological activity and/or half-life, the most extreme example being the metabolic activation of inactive prodrugs into active drugs, e.g. of codeine into morphine by CYP2D6. The principal organs of drug metabolism are the liver and the small intestine. Drugs completely inactivated during the s first-paszt hrough these organs must be given parenterally, similarly to poorly absorbed drugs.