Antipsychotics (APs) are a class of psychotrophic medication primarily used to manage psychosis (including delusions, hallucinations, paranoia or disordered thought), principally in schizophrenia but also in a range of other psychotic disorders. Biotransformation is a major mechanism for APs elimination. Most APs undergo biotransformation, or metabolism, after they enter the body. There are three phases of APs metabolism. Cytochrome P450 (CYP) monooxygenase (mixed function oxidase) plays a central role in the most APs biotransformation. CYP’s functional activity depends on gene-drug and drug-drug interaction and influences on occurrence of adverse drug reactions (ADRs). So, it is extremely important for a practicing psychiatrist to know the oxidation pathway of APs, since most of them are metabolized in the liver and this is important both to prevent ADRs and to avoid unwanted drug-drug interactions, which will undoubtedly increase the effectiveness and safety of AP therapy.