Inclusion Criteria:  Diagnosed Major Depressive Disorder Starting monotherapy with sertraline Signed written informed consent  Exclusion Criteria:  Patient's requests to leave the study Patients who had taken sertraline before Dementia Severe liver function impairment (abnormal AST/ALT ratio) Severe kidney function impairment (abnormal creatinine clearance) History of drug addiction (sporadic use is permitted) Suicide risk Patients who are taking strong CYP2C19 inhibitors Severe adverse drug reaction