Inclusion Criteria:  18-55 years of age. Diagnostic criteria for Opioid Use Disorder (OUD) moderate-severe (304.00) as per DSM-V, including physiological dependence and not currently seeking treatment for OUD. Self-reported opioid use for nontherapeutic purposes; and positive urine drug screen for opioids. Physically healthy. Normal body weight/Within 20% of body weight (for appropriate frame) according to 1983 Metropolitan Weight tables. Able to perform study procedures.  Females must be either:  Post-menopausal (amenorrhea for at least 12 consecutive months), surgically sterile -or Women of childbearing potential must agree to use an acceptable double-barrier method of contraception during screening and study participation. Must smoke < three cannabis cigarettes three times a week (or the vaping equivalent) for the four weeks before screening.  Exclusion Criteria:  Seeking treatment for Opioid Use Disorder. Current or history of a psychiatric condition that would affect participants' ability to provide informed consent (e.g., mood disorder with functional impairment or schizophrenia) or make participant hazardous for the participant (e.g., recent suicidal ideation) or staff (e.g., significant history of violence). Current DSM-V diagnosis of substance use disorders requiring medically managed detoxification, other than OUD (e.g., alcohol or benzodiazepine dependence). Medical condition resulting in chronic pain (>3 months). Clinically significant abnormality on physical examination, vital signs, screening laboratory tests, or 12- lead ECG. Significant cardiovascular, hepatic, renal, respiratory, gastrointestinal, endocrine, immunologic, dermatologic, hematologic, or neurologic disorder. Any surgical, or medical condition that may interfere with the absorption, distribution, metabolism, or excretion of the study drugs. Baseline hypotension, orthostatic hypotension or syncope, hypertension (blood pressure > 140/90), pulmonary hypertension or heart disease.  Any of the following values for laboratory tests:  positive pregnancy test, hemoglobin < 12 g/dL in males and < 11 g/dL in females, neutrophil count < 1.0 × 109/L, platelet count < 75 × 109/L, creatinine clearance < 50 ml/min per modified Cockcroft-Gault equation, aspartate aminotransferase or alanine aminotransferase > 3.0 × upper limit of normal. Hypersensitivity to opioids, history of significant adverse reactions to cannabinoids, and allergy or contraindication to any other drugs administered as a part of this investigation. Use of an investigational agent within 30 days.