A Trial to Evaluate the Efficacy, Safety & Tolerability of Brexpiprazole in the Maintenance Treatment of Adults With Major Depressive Disorder

Inclusion Criteria

• Participants with both a diagnosis of recurrent major depressive disorder, and in a current major depressive episode of ≥ 8 weeks in duration, as defined by Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) and confirmed by both the Mini International Neuropsychiatric Interview (MINI) and an adequate clinical psychiatric evaluation.
• Participants must have reported a history for the current major depressive episode of an inadequate response to 1 or 2 adequate antidepressant treatments, and participants must currently be taking a protocol-mandated antidepressant treatment at an adequate dose and duration, and most not have reported ≥ 50% improvement. For participants who are currently on an adequate dose of protocol-mandated antidepressant therapy (ADT), but for an inadequate duration, can use the screening period to achieve adequate duration. At Phase A baseline visit, all participants must have either 2 or 3 documented inadequate responses to antidepressant treatment in total for the current episode as defined by the Massachusetts General Hospital Antidepressant Treatment Response Questionnaire (ATRQ).
• Participants with a Hamilton Rating Scale for Depression (HAM-D17) total score ≥ 18 at the screening visit, and Phase A baseline visits.
• Participants willing to discontinue all prohibited psychotropic medications to meet protocol-required washouts prior to and during the trial period.

Exclusion Criteria

• Females who are breast-feeding and/or who have a positive pregnancy test result prior to receiving investigational medicinal product (IMP).
• Sexually active males or females of childbearing potential who do not agree to practice 2 different methods of birth control or remain abstinent during the trial and for 30 days after the last dose of IMP.
• Participants who report treatment with adjunctive antipsychotic medication with an antidepressant for a minimum of 3 weeks during the current major depressive episode.
• Participants who report allergies or an intolerability (lifetime treatment history) to trial-provided ADTs that have not been prescribed to the participant during the current major depressive episode.
• Participants who have received electroconvulsive therapy (ECT) for the current major depressive episode.
• Participants who have had an inadequate response to ECT at any time in the past or who have had a vagus nerve stimulation or deep brain stimulation device implanted at any time for the management of treatment-resistant depression. Participants who have had transcranial magnetic stimulation during the current major depressive episode.
• Participants with a current need for involuntary commitment or who have been hospitalized within 4 weeks of screening for the current major depressive episode.
• Participants with a primary DSM-5 diagnosis of:
• Schizophrenia Spectrum and Other Psychotic Disorders
• Bipolar and Related Disorders
• Obsessive Compulsive Disorders
• Feeding and Eating Disorders
• Neurocognitive Disorders
• Panic Disorder
• Post-Traumatic Stress Disorder
• Participants with a current DSM-5 diagnosis of borderline, antisocial, paranoid, schizoid, schizotypal, or histrionic personality disorder or intellectual disability.
• Participants experiencing hallucinations, delusions, or any psychotic symptomatology in the current major depressive episode.
• Participants receiving new onset psychotherapy (individual, group, marriage or family therapy) within 42 days of screening or at any time during participation in the trial.
• Participants who have met DSM-5 criteria for substance use disorder (moderate or severe) within the past 60 days; including alcohol and benzodiazepines, but excluding nicotine.
• Participants with hypothyroidism or hyperthyroidism (unless condition has been stabilized with medications for at least the past 90 days) and/or an abnormal result for free T4 at screening.
• Participants who currently have clinically significant ne