Brexpiprazole (OPC-34712) as an Adjunctive Treatment in Active Adults, 18 to 35 Years Old, With Major Depressive Disorder Who Are in a School or Work Environment

Main Inclusion Criteria: Have a diagnosis of a single or recurrent, nonpsychotic episode of MDD as defined by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) and confirmed by both the Mini International Neuropsychiatric Interview (M.I.N.I.) and an adequate clinical psychiatric evaluation. Have a treatment history of an inadequate ADT response to at least 1 ADT (but not \> 3) for the current episode. Have received a single, trial-approved, SSRI or SNRI at an adequate dose for ≥ 6 weeks prior to screening. Are 18 to 35 years old at the time of consent (inclusive, and outpatients only). Are (and will be) working 20 hours or more per week or a student taking 6 credit hours or more during the trial period, however minor deviations from the "part-time" concept may be acceptable on a case-by-case basis based on approval of the medical monitor. Have a Hamilton Depression Rating Scale (HAM-D)- 17-item Total Score ≥ 18 at screening and baseline. Have a Sheehan Disability Scale (SDS) 3-item mean score ≥ 5 at baseline. Main Exclusion Criteria: Subjects with any of the following current Axis I DSM-IV-TR diagnoses: delirium, dementia, amnestic, or other cognitive disorders; schizophrenia, schizoaffective disorder, or other psychotic disorders; bipolar I disorder, bipolar II disorder, or bipolar disorder not otherwise specified (NOS); eating disorders (including anorexia nervosa or bulimia); obsessive compulsive disorder; panic d…