A Study to Evaluate the Abuse Potential of Oxymorphone Compared to Other Mu Opioid Agonists.

Inclusion Criteria: 1. Able to understand and provide signed and dated written consent. 2. Self-reported opioid use for nontherapeutic purposes on at least 21 days in the 30 days prior to screening, physical dependence on opioids, recent intravenous opioid use, and meeting DSM 5 criteria for moderate-severe opioid use disorder. 3. Positive urine drug screen for opioids (those who are in a methadone or buprenorphine treatment program are ineligible; physical dependence on street methadone or buprenorphine are also exclusionary so participants must produce at least one methadone- or buprenorphine-negative urine during screening). 4. ≥ 21 and ≤ 55 years of age. 5. Body mass index (BMI) ≥ 18 and ≤ 35 kg/m2 and weight ≥ 50 kg (110 pounds). 6. Otherwise healthy as determined by the investigator. 7. Demonstrate understanding how to complete the self-administration tasks and VAS Questionnaire. 8. Women of childbearing potential must not be pregnant or breastfeeding at screening. 9. Willing and able to comply with all testing requirements defined in the protocol. participation in the Study Treatment Phase: 1. During the Study Qualification Phase, on the bipolar 100--mm Drug Liking VAS, the subject must provide Emax ≥ 40 mm and \< 60 mm following placebo and, following morphine 56 mg/70 kg, i.v., Emax ≥ 60 mm and ≥ 15 mm closer to "Strong Liking" than the Emax to placebo. 2. In the judgment of the investigator, the subject is able to tolerate the i.v., opioids administered in the study, including the ability to complete most pharmacodynamics assessments administered post--dose. 3. In the judgment of the study staff, the subject's general behavior during the Study Qualification Phase suggests the ability to successfully complete the Study Treatment Phase. Exclusion Criteria: 1. History of a medical or psychiatric disorder that would prevent successful completion of the study. 2. Current DSM-5 diagnosis of substance use disorders requiring medical management other than OUD. 3. Suicidal ideation or intent with or without a plan at Screening or within 6 months prior to Screening (i.e., answering "Yes" to questions 4 and/or 5 on the Suicidal Ideation section of the Columbia Suicide Severity Rating Scale). 4. Currently seeking or participating in treatment for substance use disorder. 5. Physically dependent on drugs of abuse (other than opioids, nicotine, or caffeine) or alcohol. 6. Medically important deviation from normal limits on physical examination, vital signs, screening laboratory tests, or 12--lead ECG. 7. Significant cardiovascular, hepatic, renal, respiratory, gastrointestinal, endocrine, immunologic, dermatologic, hematologic, or neurologic disorder. 8. Any surgical, or medical condition that may interfere with the absorption, distribution, metabolism, or excretion of the test drug. 9. Family history of long QT syndrome and/or unexpected sudden cardiac death or is known to have QTc \> 500 ms at screening. 10. Used an investigational agent within 30 days or 5 therapeutic half-lives of that agent, whichever is longer, prior to the first dose of study drug. 11. Hypersensitivity to opioids or any drug intended for use in this study. 12. Acute gastrointestinal symptoms (e.g., nausea, vomiting, fever, or Diarrhea unrelated to opioid withdrawal) ≤ 7 days before Day 1. 13. Any of the following values for laboratory tests at Screening: 1. A positive pregnancy test in women of childbearing potential. 2. Hemoglobin \< 11 g/dL in males and \< 10 gm/dL in females. 3. Neutrophil count \< 1.0 × 109/L. 4. Platelet count \< 75 × 109/L. 5. Creatinine clearance \< 50 ml/min per modified Cockcroft-Gault equation. 6. Aspartate aminotransferase or alanine aminotransferase \> 3.0x upper limit of normal.