An outpatient study to evaluate the safety and efficacy of cariprazine as adjunct to Antidepressant Therapy (ADT) in patients with Major Depressive Disorder (MDD) who have an inadequate response to antidepressant alone. This clinical study will be comparing cariprazine + ADT with placebo + ADT in outpatients with a diagnosis of MDD and an inadequate response to ADT in the current episode. The study will consist of approximately 2 weeks of screening and washout followed by 8 weeks of double-blind treatment followed by a 1 week safety follow-up.