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, vitalsigns, and 12-lead electrocardiogram (ECG) performed at screening and baseline

• Have a Hamilton depression rating Scale 17 item (HDRS-17) total score of 20 orhigher at the first and second screening interviews and must not demonstrate aclinically significant improvement (that is, an improvement of more than 20 percent [%] on their HDRS-17 total score) between the first and the second independentHDRS-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 thestructural 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 depressionprior to 55 years of age

• Is currently receiving and tolerating well any one of the following selectiveserotonin reuptake inhibitor (SSRI) or serotonin-norepinephrine reuptake inhibitor (SNRI) for depressive symptoms at screening, in any approved formulation andavailable in the participating country/territory: citalopram, duloxetine,escitalopram, fluvoxamine, fluoxetine, milnacipran, levomilnacipran, paroxetine,sertraline, venlafaxine, desvenlafaxine at a stable dose (at or above the minimumtherapeutic dose per Massachusetts General Hospital Antidepressant TreatmentResponse Questionnaire [MGH-ATRQ] for at least 6 weeks. The current antidepressantcannot be the first antidepressant treatment for the first lifetime episode ofdepression

• Participant's current major depressive episode, and antidepressant treatmentresponse in the current depressive episode, must all be confirmed by the SiteIndependent Qualification Assessment

Exclusion Criteria:

• Have had in the current depressive episode, no response (treatment failure) to 5 ormore antidepressant treatments including the current SSRI/SNRI (that is, the onepresumed to be continued in the treatment phase) assessed using the MGH-ATRQ

• Has a history or evidence of clinically meaningful noncompliance with currentantidepressant therapy

• Has a history of moderate-to-severe substance use disorder including alcohol usedisorder according to diagnostic and statistical manual of mental disorders-5thedition (DSM-5) criteria within 6 months before screening

• Has had in the current episode an inadequate response to adequate course ofintravenous or intranasal ketamine or esketamine, electroconvulsive therapy (thatis, at least 7 treatments), vagal nerve stimulation, or deep brain stimulationdevice

• 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 startof the Screening Phase, per the investigator's clinical judgment or based on theColumbia Suicide Severity Rating Scale (C-SSRS), corresponding to a response of "Yes" on Item 4 (active suicidal ideation with some intent to act, without specificplan) or Item 5 (active suicidal ideation with specific plan and intent), or ahistory of suicidal behavior within the past 6 months prior to the start of theScreening Phase. Participants reporting suicidal ideation with intent to act orsuicidal behavior at baseline should be excluded

• Has one or more of the following diagnoses: a) A diagnostic and statistical manualof mental disorders-5th edition (DSM-5) diagnosis (which has been the primary focusof psychiatric treatment within the past 2 years) of any of the following: panicdisorder, 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 (lifetime) DSM-5 diagnosis of: a psychotic disorder or majordepressive disorder (MDD) with psychotic features, bipolar or related disorders,intellectual disability, autism spectrum disorder, borderline personality disorder,antisocial personality disorder, histrionic personality disorder, narcissisticpersonality disorders, somatoform disorders