Inclusion Criteria:  Diagnosis of major depression, recurrent, severe without psychotic symptoms according to criteria in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-V). Must be diagnosed with Treatment resistant depression.  18 years old and up Patients had a clinically meaningful response to a course of IV racemic ketamine  Exclusion Criteria:  Active substance abuse, psychosis, significant medical comorbidities, or axis II diagnosis that would interfere with the reliability of outcome measures or response to pharmacotherapy.