A Study to Evaluate the Efficacy, Safety, and Tolerability of Flexible 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 subjects know what treatment the subject is receiving), active-controlled, multicenter study (more than 1 study site) in subjects with TRD to assess the efficacy, safety, and tolerability of flexible 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). Subjects who rollover into a long-term maintenance study will not participate in the Follow-up Phase. The antidepressant treatment, as well as any other ongoing medications being taken for depression at screening (including adjunctive/ augmentation therapies), will continue unchanged, at the same dosage, from the start of Week 1 through the end of Week 4 of the screening/prospective observational phase. Subjects' safety will be monitored throughout the study.