Cytochrome P450 2D6<unk>  is an enzyme that in humans is encoded by the<unk>  gene.<unk>  is primarily expressed in the liver. It is also highly expressed in areas of the central nervous system, including the substantia nigra.<unk> , a member of the cytochrome P450 mixed-function oxidase system, is one of the most important enzymes involved in the metabolism of xenobiotics in the body. In particular,<unk>  is responsible for the metabolism and elimination of approximately 25% of clinically used drugs, via the addition or removal of certain functional groups – specifically, hydroxylation, demethylation, and dealkylation.<unk>  also activates some prodrugs. This enzyme also metabolizes several endogenous substances, such as hydroxytryptamines, neurosteroids, and both m-tyramine and p-tyramine which<unk>  metabolizes into dopamine in the brain and liver. Considerable variation exists in the efficiency and amount of<unk>  enzyme produced between individuals. Hence, for drugs that are metabolized by<unk>  (that is, are<unk>  substrates), certain individuals will eliminate these drugs quickly (ultrarapid metabolizers) while others slowly (poor metabolizers). If a drug is metabolized too quickly, it may decrease the drug's efficacy while if the drug is metabolized too slowly, toxicity may result. So, the dose of the drug may have to be adjusted to take into account of the speed at which it is metabolized by<unk> . Other drugs may function as inhibitors of<unk>  activity or inducers of<unk>  enzyme expression that will lead to decreased or increased<unk>  activity respectively. If such a drug is taken at the same time as a second drug that is a<unk>  substrate, the first drug may affect the elimination rate of the second through what is known as a drug-drug interaction.
CYP2D6
CYP2C19
CYP1A2
CYP2C8
CYP2C9
CYP3A5
CYP3A4
CYP2J2