Of particular importance in the treatment of psychotic disorders, such as schizophrenia and bipolar disorder with psychotic features, CYP2D6 is critical in the metabolism of risperidone, one of the most widely used atypical antipsychotic agents. Several studies have assessed CYP450 genotype in patients who were able to tolerate risperidone versus patients who were not able to. The CYP2D6 poor metabolizer phenotype was shown to be associated with risperidone side effects and discontinuation of the drug. Recent evidence suggest that intermediate metabolizers also tend to have higher rates of side effects when taking regular doses of risperidone.