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

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.