Low Dose Intravenous Ketamine in Treatment Resistant Depression Patients

Inclusion Criteria: * Be between 18-60 years of age * Meet criteria for Treatment Resistant Depression (defined as two or more unsuccessful trials of antidepressants at an adequate dose for at least 4 weeks) Exclusion Criteria: * Diagnosed with intellectual disability, eg. Mental retardation, neurodegenerative diseases, eg. Early onset neurocognitive disturbances such as frontotemporal dementia or behavioral disorders, eg. adult onset Attention Deficit Hyperactivity Disorder, * Diagnosed with Bipolar Disorder (BD), * Diagnosed with personality disorders, * Previously or currently diagnosed with psychosis (schizoaffective disorder -SAD) or schizophrenia - SCZ), * Current major medical problems that affect brain anatomy, neurochemistry, or function, e.g., obstructive sleep apnea requiring Continuous Positive Airway Pressure (CPAP), liver insufficiency, kidney insufficiency, cardiovascular problems, systemic infections, cancer, auto-immune diseases, and any brain disorder (seizure disorder, stroke, dementia, degenerative neurologic diseases); history of any brain diseases, including seizures, stroke, meningitis, encephalitis, dementia, degenerative brain diseases, and head injury with loss of consciousness for any period of time, * Diagnosed specifically with a cardiovascular disorders such as Hypertension, Arrhythmias, Chronic Heart Failure, Myocardial Infarction (MI) or suffering from Chronic Obstructive Pulmonary Disease (COPD) or asthma. Cardiac clearance prior to enrolling in the study and medical records from physician will be required per patient's Primary Care Physician. * Patients with increased risk of laryngospasm, active upper respiratory infections, respiratory depression, increased intracranial pressure, thyroid disease, or porphyria, * Current substance abuse or dependence. Only patients who achieved stable, full remission for at least 6 months will be included * Pregnancy or Breast feeding. All female in reproductive age will undergo pregnancy tests. Female participants will be required to provide evidence of use of contraceptives during the course of the study, * Unable to understand the design and requirements of the study. * Unable to sign the informed consent for any reason.