A Study to Evaluate the Efficacy, Safety, and Tolerability of Fixed Doses of Intranasal Esketamine Plus an Oral Antidepressant in Adult Participants With Treatment-resistant Depression

The purpose of this study is to compare the efficacy and safety of switching treatment-resistant depression (TRD) participants from a prior antidepressant treatment (to which they have not responded) to either intranasal esketamine plus a new oral antidepressant or switching to a new oral antidepressant plus intranasal placebo.

This is a randomized, double-blind (neither the researchers nor the participants know what treatment the participant is receiving), active-controlled, multicenter study (more than 1 study site) in participants with TRD to assess the efficacy, safety, and tolerability of fixed doses of intranasal esketamine plus a newly initiated oral antidepressant compared with a newly initiated oral antidepressant (active comparator) plus intranasal placebo. The study will consist of 3 phases: Screening/Prospective Observational Phase (4-7 weeks), Double-blind Induction Phase (4-weeks), Follow-up Phase (24-weeks). Participants who rollover into a long-term maintenance study will not participate in the Follow-up Phase. At the start of the screening/prospective observational phase, the participant must have had documented non-response to at least 1 antidepressant treatment (based on Massachusetts General Hospital - Antidepressant Treatment Response Questionnair \[MGH-ATRQ\]) in the current episode of depression, and participant is taking a different oral antidepressant treatment on the MGH-ATRQ for at least the previous 2 weeks at or above the minimum therapeutic dose. This antidepressant treatment, as well as any other ongoing medications being taken for depression at screening (including adjunctive/ augmentation therapies), will continue from the start of Week 1 through the end of Week 4 of the screening/prospective observational phase. Participants will be randomly assigned to receive Intranasal esketamine (56 milligrams \[mg\]), Intranasal esketamine (84 mg), or Intranasal placebo. In addition, each participant will be assigned to receive 1 of 4 oral antidepressant medications from 2 different classes of antidepressant treatments, a Selective Serotonin Reuptake Inhibitor (SSRI) (escitalopram or sertraline) or a Serotonin and Norepinephrine Reuptake Inhibitor (SNRI) (duloxetine or venlafaxine extended release \[XR\]), initiated on Day 1 and continued through the double-blind induction phase. Participants will be primarily evaluated for improvement in depressive symptoms as assessed by change in Montgomery-Asberg Depression Rating Scale (MADRS) total score at Week 4. Participants' safety will be monitored throughout the study.

Eligibility Criteria:
Inclusion Criteria:

* At the time of signing the informed consent form (ICF), participant must be a man or woman 18 (or older if the minimum legal age of consent in the country in which the study is taking place is greater than \[\>\]18) to 64 years of age, inclusive
* At the start of the screening/prospective observational phase, participant must meet the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) diagnostic criteria for single-episode major depressive disorder (MDD) (if single-episode MDD, the duration must be greater than or equal to \[\>=\] 2 years) or recurrent MDD, without psychotic features, based upon clinical assessment and confirmed by the Mini-International Neuropsychiatric Interview (MINI)
* At the start of the screening/prospective observational phase, participant must have an Inventory of Depressive Symptomatology-Clinician rated ( IDS-C30) total score of greater than or equal to (\>=) 34
* At the start of the screening/prospective observational phase, participants must have had non-response (less than or equal to \[\<=25\] percent \[%\] improvement) to \>=1 but less than or equal to (\<=) 5 (if current episode is \>2 years, upper limit is applicable to only the last 2 years) oral antidepressant treatments taken at adequate dosage and for adequate duration, as assessed using the Massachusetts General Hospital - Antidepressant Treatment Response Questionnaire (MGH-ATRQ) and documented by medical history and pharmacy/prescription records, for the current episode of depression.

Participant is taking a different oral antidepressant treatment on the MGH-ATRQ for at least the previous 2 weeks at or above the minimum therapeutic dose

- The participant's current major depressive episode, depression symptom severity (Week 1 MADRS total score \>=28 required), and antidepressant treatment response in the current depressive episode, must be confirmed using a Site Independent Qualification Assessment

Exclusion Criteria:

* Participants who have previously demonstrated nonresponse of depressive symptoms to esketamine or ketamine in the current major depressive episode, to all 4 of the oral antidepressant treatment options available for the double-blind induction phase (i.e, duloxetine, escitalopram, sertraline, and venlafaxine extended release \[XR\]) in the current major depressive episode (based on MGH-ATRQ), or an adequate course of treatment with electroconvulsive therapy (ECT) in the current major depressive episode, defined as at least 7 treatments with unilateral/bilateral ECT
* Participant has received vagal nerve stimulation (VNS) or has received deep brain stimulation (DBS) in the current episode of depression
* Participant has a current or prior DSM-5 diagnosis of a psychotic disorder or MDD with psychotic features bipolar or related disorders (confirmed by the MINI), obsessive compulsive disorder (current only), intellectual disability (DSM-5 diagnostic codes 317, 318.0, 318.1, 318.2, 315.8, and 319), autism spectrum disorder, borderline personality disorder, antisocial personality disorder, histrionic personality disorder, or narcissistic personality disorder
* Participant has homicidal ideation/intent, per the investigator's clinical judgment, or has suicidal ideation with some intent to act within 6 months prior to the start of the screening/prospective observational phase, per the investigator's clinical judgment or based on the Columbia Suicide Severity Rating Scale (C-SSRS)
* Participants with history of moderate or severe substance or alcohol use disorder according to DSM-5 criteria