A Study of Esketamine Nasal Spray Plus a New Standard-of-care Oral Antidepressant or Placebo Nasal Spray Plus a New Standard-of-care Oral Antidepressant in Adult and Elderly Participants With Treatment-resistant Depression

Participants will receive 28 mg esketamine as nasal spray (Initial dose for elderly participants with 65-74 years of age on Day 1 and then uptitrated to 56 mg on Day 4).

Participants will receive 56 mg esketamine as nasal spray (Initial dose for participants with 18-64 years of age) on Day 1. The dose may be increased/may remain same based on the efficacy and tolerability. Participants with 65 to 74 years of age will receive esketamine 56 mg from Day 4 onwards.

Participants may receive 84 mg (maximum uptitrated esketamine dose). The dose may be decreased/may remain same based on the efficacy and tolerability.

Participants will receive matching placebo as nasal spray.

Escitalopram can be selected as the oral antidepressant medication based on investigator's discretion. The initial dose for escitalopram is 5 mg once daily (for elderly participants) and 10 mg once daily (for adults). The dose may be increased to 10 mg (for elderly participants) and 20 mg (for adults) once daily at the discretion of treating physician/investigator.

Sertraline can be selected as the oral antidepressant medication based on investigator's discretion. The initial dose for sertraline is 50 mg once daily and may be increased up to 200 mg once daily.

Duloxetine can be selected as the oral antidepressant medication based on investigator's discretion. The initial dose for duloxetine is 60 mg once daily and may be increased to 120 mg once daily.

Mirtazapine can be selected as the oral antidepressant medication based on investigator's discretion. The initial dose for mirtazapine is 15 to 30 mg once daily and may be increased to 45 mg once daily.

Agomelatine can be selected as the oral antidepressant medication based on investigator's discretion. The initial dose for agomelatine is 25 mg once daily and may be increased to 50 mg once daily after 2 weeks.

Bupropion can be selected as the oral antidepressant medication based on investigator's discretion. The initial dose for bupropion is 150 mg once daily and may be increased to 300 mg once daily after 4 weeks.

Trazodone prolonged release can be selected as the oral antidepressant medication based on investigator's discretion. The initial dose for trazodone prolonged release is 75 to 150 mg once or twice daily and may be increased up to 450 mg (adults) and 300 mg (elderly).