Ketamine for OUD and Comorbid Depression (OUDCD)

Inclusion Criteria * From NHS prescreen (no contact, Study Day 0): Between the ages of 18 to 65 years old * From NHS prescreen (no contact, Study Day 0): Daily use of illicit opioids * From NHS prescreen (no contact, Study Day 0): Fulfillment of DSM-5/ICD-10 criteria for moderate-to-severe opioid or heroin use disorder * From NHS prescreen (no contact, Study Day 0): Acceptance into methadone maintenance care for treatment of opioid or heroin use disorder * From screening for study eligibility (Study Contact Day 1): A total of 10 or more points on the PHQ-9 * From screening for study eligibility (Study Contact Day 1): Have had no prior sustained experience/dependence on ketamine or PCP (i.e., must answer "no" to all four questions on the ketamine/PCP screen) Exclusion Criteria * From NHS prescreen (no contact, Study Day 0): Patients transferring from another program of opioid agonist treatment * From NHS prescreen (no contact, Study Day 0): Electrocardiogram (ECG) findings of tachycardia, prior myocardial infarction, myocardial ischemia, or aberrant conduction * From NHS prescreen (no contact, Study Day 0): Self-report of recent prescribed or illicit benzodiazepine use ("Xannies", or "bars") * From NHS prescreen (no contact, Study Day 0): Urine screen positive for pregnancy * From NHS prescreen (no contact, Study Day 0): Stage 2 hypertension, defined by a systolic blood pressure (SBP) \> 140 mmHg or a diastolic blood pressure (DBP) \> 90 mmHg * From NHS prescreen (no contact, Study Day 0): Clinically significant abnormal laboratory values, physical exam findings or self-reported medical conditions for which a transient increase in blood pressure could be significantly detrimental (e.g., cardiovascular disease), as determined by the evaluating intake physician * From NHS prescreen (no contact, Study Day 0): Any clinically significant abnormal findings from intake health and physical examination * From NHS prescreen (no contact, Study Day 0): Any indication of serious mental illness or psychiatric disorder from the attending's evaluation notes * From Liver Function Screen (Study Contact Day 2): Baseline alkaline phosphatase \> 2.5 times the upper limit of normal * From Liver Function Screen (Study Contact Day 2): Baseline aspartate aminotransferase \> 3 times the upper limit of normal * From Psychiatric Evaluation (Study Contact Day 2) Current or previous recreational use of ketamine or PCP * From Psychiatric Evaluation (Study Contact Day 2): Subjects who meet DSM-5 criteria for current bipolar disorder * From Psychiatric Evaluation (Study Contact Day 2): Past or current presence of psychotic symptoms, or diagnosis of a lifetime psychotic disorder including schizophrenia or schizoaffective disorder * Subjects who meet DSM-5 criteria for current or history of psychotic spectrum disorders