Study to Assess the Efficacy and Safety of NBI-1065845 as an Adjunctive Treatment in Participants With Major Depressive Disorder (MDD)

Key Inclusion Criteria:

• Participant has a primary diagnosis of recurrent MDD (moderate or severe) orpersistent depressive disorder.

• Participant has had an inadequate response to oral antidepressant treatments in thecurrent episode of depression.

• Participant must have been taking oral antidepressants for at least 8 weeks and iswilling to continue the same oral antidepressants at the same dose and frequency ofadministration throughout participation in the study.

• Total Hamilton Depression Rating Scale-17 Item (HAM-D17) score ≥22 at screening andat study baseline (Day 1).

• Willing and able to comply with all study procedures and restrictions in the opinionof the investigator.

Key Exclusion Criteria:

• A current or prior psychiatric disorder diagnosis in the last 1 year that was theprimary focus of treatment other than MDD.

• Are considered by the investigator to be at imminent risk of suicide or injury toself or others.

• Participants depressive symptoms have previously demonstrated nonresponse toelectroconvulsive therapy (ECT) in the current major depressive episode.