A Study of Aticaprant 10 Milligrams (mg) as Adjunctive Therapy in Adult Participants With MDD With Moderate-to-severe Anhedonia and Inadequate Response to Current Antidepressant Therapy

Inclusion Criteria

• Be medically stable on the basis of physical examination, medical history, vital signs, and 12-lead electrocardiogram (ECG) performed at screening and baseline
• Have a Hamilton depression rating Scale 17 item (HDRS-17) total score of 20 or higher at the first and second screening interviews and must not demonstrate a clinically significant improvement (that is, an improvement of more than 20 percent [%] on their HDRS-17 total score) between the first and the second independent HDRS-17 assessments
• Meet Diagnostic and Statistical Manual of Mental Disorders-5th edition (DSM-5) diagnostic criteria for recurrent or single episode major depressive disorder (MDD), without psychotic features, based upon clinical assessment and confirmed by the structural interview for DSM-5 Axis I disorders-clinical trials version (SCID-CT). Participants 65 years of age or older must have had the first onset of depression prior to 55 years of age
• Is currently receiving and tolerating well any one of the following selective serotonin reuptake inhibitor (SSRI) or serotonin-norepinephrine reuptake inhibitor (SNRI) for depressive symptoms at screening, in any approved formulation and available in the participating country/territory: citalopram, duloxetine, escitalopram, fluvoxamine, fluoxetine, milnacipran, levomilnacipran, paroxetine, sertraline, venlafaxine, desvenlafaxine at a stable dose (at or above the minimum therapeutic dose per Massachusetts General Hospital Antidepressant Treatment Response Questionnaire [MGH-ATRQ] for at least 6 weeks. The current antidepressant cannot be the first antidepressant treatment for the first lifetime episode of depression
• Participant's current major depressive episode, and antidepressant treatment response in the current depressive episode, must all be confirmed by the Site Independent Qualification Assessment

Exclusion Criteria

• Have had in the current depressive episode, no response (treatment failure) to 5 or more antidepressant treatments including the current SSRI/SNRI (that is, the one presumed to be continued in the treatment phase) assessed using the MGH-ATRQ
• Has a history or evidence of clinically meaningful noncompliance with current antidepressant therapy
• Has a history of moderate-to-severe substance use disorder including alcohol use disorder according to diagnostic and statistical manual of mental disorders-5th edition (DSM-5) criteria within 6 months before screening
• Has had in the current episode an inadequate response to adequate course of intravenous or intranasal ketamine or esketamine, electroconvulsive therapy (that is, at least 7 treatments), vagal nerve stimulation, or deep brain stimulation device
• Has current, or a history (past 6 months), of seizures
• Has a current homicidal ideation/intent, per the investigator's clinical judgment, or has suicidal ideation with some intent to act within 3 months prior to the start of the Screening Phase, per the investigator's clinical judgment or based on the Columbia Suicide Severity Rating Scale (C-SSRS), corresponding to a response of "Yes" on Item 4 (active suicidal ideation with some intent to act, without specific plan) or Item 5 (active suicidal ideation with specific plan and intent), or a history of suicidal behavior within the past 6 months prior to the start of the Screening Phase. Participants reporting suicidal ideation with intent to act or suicidal behavior at baseline should be excluded
• Has one or more of the following diagnoses: a) A diagnostic and statistical manual of mental disorders-5th edition (DSM-5) diagnosis (which has been the primary focus of psychiatric treatment within the past 2 years) of any of the following: panic disorder, generalized anxiety disorder social anxiety disorder, specific phobia; b) A current (in the past year) DSM-5 diagnosis of: obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), anorexia nervosa, bulimia nervosa; c) A current or prior (lifet