A Study to Evaluate the Safety and Efficacy of ALKS 7290 as an Adjunctive Therapy to Antidepressants in Adult Participants With Major Depressive Disorder

Inclusion Criteria: * Meets the DSM-5 criteria for MDD, as confirmed by both MINI and an adequate clinical psychiatric evaluation. * Is otherwise healthy as determined by medical evaluation, including medical history, physical examination, laboratory tests, and cardiac monitoring. * Participants must be stable on permitted medication prior to screening. * An inadequate response to an adequate dosage of antidepressant therapy in the current depressive episode. * Symptoms of depression that are considered moderate to severe, based on assessments completed with the study team during both screening and baseline visits. * Has a BMI within 18 to 35 kg/m2 at Screening Exclusion Criteria: * Diagnosis of schizophrenia, schizoaffective disorder, or bipolar I or II disorder, moderate to severe substance use disorder * Significant problems with memory, thinking, learning or understanding that could make it difficult to complete study activities or follow study instructions. This includes conditions such as dementia or other disorders affecting thinking and memory that have been present within the past two years. * Participant poses a current suicide risk as assessed by the Investigator or as confirmed by the C-SSRS * Any other psychiatric condition that could interfere with participation in the study.