Thus, in the present study involving patients with schizophrenia, we investigated whether seven single nucleotide polymorphisms (SNPs) in CYP1A2, UGT1A4, and ABCB1 are associated with side effects of olanzapine, including decreased ANS activity, to clarify the factors that affect interindividual differences in decreased ANS activity during olanzapine therapy and to provide safer medication that can be tailored to individual genotypes. Here, ABCB1 is linked to schizophrenia.