This is a multicenter, randomized, double-blind, placebo-controlled, parallel, multiple dose study designed to evaluate the safety and tolerability of the co-formulation of ALKS 33 with buprenorphine (ALKS 5461) in subjects with Major Depressive Disorder (MDD) who are inadequately/partially responding to current treatment with a stable dose of a serotonin-selective reuptake inhibitor (SSRI) or serotonin-norepinephrine reuptake inhibitor (SNRI).

Inclusion Criteria:

• Male and female subjects between 18 and 65 years of age, inclusive.

• Meet Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR) criteria for MDD.

• Current episode lasting ≥8 weeks prior to screening with an inadequate/partial response to an adequate trial (defined as at least 8 weeks) of a stable dose of an SSRI or SNRI. Inadequate/partial response is defined as:

  1. A Hamilton Depression Rating Scale total score (HAM-D17) ≥14, and
  2. Less than 50% reduction in depressive symptom severity on the Massachusetts General Hospital Antidepressant Treatment Response Questionnaire (ATRQ), and
  3. Clinical Global Impression - Severity (CGI-S) score of ≥3.

Exclusion Criteria:

• Axis I diagnosis of delirium, dementia, amnestic or other cognitive disorder, schizophrenia or other psychotic disorder, bipolar I or II disorder, eating disorder, obsessive-compulsive disorder, panic disorder, or posttraumatic stress disorder.
• A clinically significant current Axis II diagnosis of borderline, antisocial, paranoid, schizoid, schizotypal, or histrionic personality disorder.
• Experiencing hallucinations, delusions, or any psychotic symptomatology in the current episode.
• The use of inducers or inhibitors of cytochrome P450 (CYP) 3A4 (prescription medications, over-the-counter [OTC] medications, or dietary supplements) within 30 days before dosing.
• Have received electroconvulsive therapy during the current MDD episode.
• Pose current suicide risk as confirmed by the Columbia Suicide Severity Rating Scale (C SSRS).
• History of intolerance or hypersensitivity to buprenorphine.
• History of allergy or hypersensitivity to opioid antagonists (eg, naltrexone, naloxone) or quinine.