Pharmacogenetic tests that allow the clinician to individualize dosage to the patient according to the activity of their metabolism are described. Pharmacogenetic aspects of the oxidative phase of antipsychotic biotransformation are reviewed. Depending on the rate of metabolism and enzyme activity of cytochrome (CYP) family (especially, CYP1 A2, CYP2D6 and CYP3A4) people can be divided into three groups: poor, rapid and ultrarapid metabolizers. Pharmacogenetic testing before the administration of therapy can be useful for choosing the optimal drug and its effective and acceptable dose for the individual patient. Along with the advantages and possibilities of pharmacogenetic testing, its difficulties and pitfalls are discussed. The authors emphasized that the investigation of cytochrome-based metabolism is only one of the components of individualized medicine.