Schizophrenia is a chronic mental disorder. It is treated with antipsychotics, which have a high risk of adverse drug reactions. Approximately 20-30% of patients with schizophrenia remain resistant to psychopharmacotherapy. Determining the individual predisposition to the response to antipsychotics and antipsychotic-induced adverse drug reactions development is possible using pharmacogenetic testing. Purpose is to present the role of pharmacogenetic testing in optimizing antipsychotic therapy. Materials and methods: The peripheral blood of patients was genotyping using real-time polymerase chain reaction. Results: This case report is about a 30- year-old female patient with paranoid schizophrenia, which had a long history of low effectiveness and poor tolerability of antipsychotics. The treatment was complicated by the pituitary microadenoma presence. According to the PGx results, the patient has a “poor transporter” phenotype, which also explains the high risk adverse drug reactions developing and therapeutic resistance while taking P- glycoprotein substrates antipsychotics. For the treatment, the antipsychotic brexpiprazole was selected, which did not have the P-glycoprotein substrate properties. It made possible to achieve paranoid schizophrenia remission and hyperprolactinemia correction. Conclusion: This case report demonstrates that wider implementation of pharmacogenetic testing into real clinical practice could help significantly improve the efficiency and safety of antipsychotic therapy.