The study will evaluate the efficacy of NBI-1065845 compared with placebo as an adjunctive treatment in participants with MDD on improving symptoms of depression.
Participant has a primary diagnosis of recurrent MDD (moderate or severe) or persistent depressive disorder.
Participant has had an inadequate response to oral antidepressant treatments in the current episode of depression.
Participant must have been taking oral antidepressants for at least 8 weeks and is willing to continue the same oral antidepressants at the same dose and frequency of administration throughout participation in the study.
Total Hamilton Depression Rating Scale-17 Item (HAM-D17) score ≥22 at screening and at study baseline (Day 1).
A current or prior psychiatric disorder diagnosis in the last 1 year that was the primary focus of treatment other than MDD.
Are considered by the investigator to be at imminent risk of suicide or injury to self or others.
Participants depressive symptoms have previously demonstrated nonresponse to electroconvulsive therapy (ECT) in the current major depressive episode.