The study will evaluate the efficacy of an experimental medication compared with placebo as an adjunctive treatment in participants with MDD on improving symptoms of depression. The entire study consists of up to 8 study visits over 10-14 weeks. Some visits may be completed virtually. The study involves various heath related procedures (such as physical exam, EKG, blood draw) and surveys/interviews. If eligible, you would then be given the study medication to take every day. You must be willing to continue your current oral antidepressants at the same dose and frequency of administration throughout participation in the study.

Who can Participate

Key Inclusion Criteria: -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). -Willing and able to comply with all study procedures and restrictions in the opinion of the investigator. Key Exclusion Criteria: -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.

Study ID