Inclusion Criteria:  Between 18 and 65 years of age at Screening Diagnosis of Major Depressive Disorder (MDD) Significant level of suicidal thoughts with active ideation and without immediate intent Failure to respond to 2 medications in the current episode  Exclusion Criteria:  Current or past history of schizophrenia, psychotic disorder, bipolar disorder, borderline personality disorder, etc. Current alcohol or substance use disorder