Aripiprazole is an atypic antipsychotic drug commonly used in the treatment of negative and positive psychotic symptoms in patients with schizophrenia, other psychotic disorders and bipolar disorder. Sagittal sinus thrombosis and transverse sinus thrombosis are the manifestations of venous thromboembolism. Warfarin is used in the treatment of venous thromboembolism. Antipsychotic treatment should be used with caution when psychotic symptoms develop in patients receiving thrombosis therapy. It is known that the risk of thrombosis increases in patients receiving antipsychotic treatment. A 32-year-old female was admitted to our outpatient unit with complaints of psychotic symptoms. The patient was using warfarin therapy for thrombosis prophylaxis. Before aripiprazole was started, INR (international normalized ratio) value was 2.18. After a week, INR value was 8. Aripiprazole treatment was stopped and INR value returned to 2.24 after a week. This report describes a 32-year-old female patient with a diagnosis of unspecified schizophrenia spectrum and other psychotic disorder according to DSM-5 who developed an increase in INR levels during aripiprazole therapy. This side effect is important because it may sometimes be life threatening and our case is the first case showing the effect of aripiprazole on INR.