Aripiprazole Augmentation Versus Switching to Different Class of Antidepressants in Major Depressive Disorder

Inclusion Criteria: * Patients who are older than 20 years of age have a diagnosis of MDD without psychotic features, as defined by DSM-IV-TR. * Patients have to report an inadequate response to a current antidepressant treatment. Inadequate response to antidepressant is defined as: total score of HDRS-17 is more than 14), despite adequate dose of current antidepressant treatment for at least 6 weeks in the current episode(co-administered with ATRQ) * Classification of antidepressants which can be included in the study(list for suggestion): Escitalopram 10\~20mg/day, fluoxetine 20\~40mg/day,paroxetine controlled release(CR) 25\~62.5mg or paroxetine 20\~40mg, sertraline 100\~150mg,bupropion XL(SR) 150\~300mg, mirtazapine 15\~45mg,venlafaxine immediate or extended release(IR or ER) 112.5\~225mg/day, duloxetine 60mg \[same criteria for generic medications as brand drugs\] Exclusion Criteria: * Those who are first episode, drug naive MDD subjects * Those who have a current Axis I diagnosis of delirium, dementia, amnestic or other cognitive disorder, schizophrenia or other psychotic disorder, bipolar 1 or 2 disorder, eating disorder, obsessive-compulsive disorder, panic disorder, or posttraumatic stress disorder * Those who have a clinically significant current Axis 2 diagnosis of borderline, antisocial, paranoid, schizoid, schizotypal, or histrionic personality disorder * Those who experience hallucinations, delusion, or any psychotic symptomatology in the current depressive episode * Those who have met DSM-IV-TR criteria for any significant substance use disorder within the past 12 months (except nicotine) * Those who have known allergy,hypersensitivity or previous unresponsiveness to aripiprazole or known intolerance to other study medications * Those who have had cognitive-behavioral therapy or other psychotherapy, or they have the potential need to be treated with them during the study periods * Those who are complicated with serious medical problem, such as severe renal, hepatic dysfunction, cardiovascular, lung, gastrointestinal, endocrine, nervous, infectious disease, or neoblastic, metabolic disease * Those who have shown previous unresponsiveness to adequate antidepressant trials more than 2 episodes or with 3 or more antidepressant treatments * Those who have chronic liver or renal disease * Those who are pregnant or brest-feeding * Those who have participated in a clinical trial with aripiprazole or any other investigational product within the past month(include randomized, double-blind, placebo-controlled or open-label study; but chart review,observational study can be enrolled) * Those who had a history of thyroid pathology, neuroleptic malignant syndrome, or serotonin syndrome * Those who have received adjunctive antipsychotic plus antidepressant for more than 3 weeks during the current episode * Those who have received electroconvulsive therapy for the current episode * Those who have shown an inadequate response to previous ECT in any episode * Those who have a suicidal risk * Those who are likely to require prohibited concomitant therapy during the trial * Those who have received treatment with a monoamine oxidase inhibitor within 2 weeks prior to enrollment