ABCG2 and schizophrenia: DNA was isolated from the peripheral blood samples of 27 patients with schizophrenia receiving clozapine maintenance treatment, and the pharmacokinetics‐related genes (CYP1A2, CYP2B6, CYP2C19, CYP2D6, CYP3A5, ABCG2, and SLCO1B1) were genotyped.