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

The purpose of this study is to evaluate the efficacy of switching adult participants with treatment-resistant depression (TRD) from a prior antidepressant treatment (to which they have not responded) to flexibly dosed intranasal esketamine (56 milligram \[mg\] or 84 mg) plus a newly initiated oral antidepressant compared with switching to a newly initiated oral antidepressant (active comparator) plus intranasal placebo, in improving depressive symptoms. Efficacy will be assessed by the change from baseline in the Montgomery Asberg Depression Rating Scale (MADRS) total score from Day 1 (before randomization) to the end of the 4-week double-blind treatment phase.