A Multiple Dose Opioid Challenge Study

Inclusion Criteria: 1. Patient had to provide written informed consent prior to the conduct of any study-related procedures. 2. Male or female, 18-55 years of age, inclusive. 3. Patients with a diagnosis of moderate or severe opioid use disorder (DSM-V) who were physically dependent on intravenous (IV) or insufflated opioids, and who were willing to undergo short-term BPN treatment. 4. Self-reported opioid-use of a minimum of 21 days in the 30 days prior to Screening. 5. Positive UDS for opioids at Screening or at check-in. If UDS was not positive, patients had to present with physical signs of withdrawal, as determined by the Investigator. The Investigator may have administered a naloxone challenge, in order to confirm opioid dependence at the Investigator's discretion. 6. Female patients of childbearing potential had to be willing to use a reliable method of contraception during the entire study (Screening Visit to Follow-up Phone Call). 7. Female patients of non-childbearing potential were surgically sterile (i.e., had undergone complete hysterectomy, bilateral oophorectomy, or tubal ligation) or in a menopausal state (at least 1 year without menses), as confirmed by follicle stimulating hormone (FSH) levels. 8. Male patients with female partners of childbearing potential had to agree to use a reliable method of contraception from Screening Visit through at least 3 months after the last dose of study drug. Male patients also must have agreed not to donate sperm during the study through at least 3 months after the last dose of study drug. 9. Were willing and able to comply with the study requirements (including blood sampling), complete study assessments, visit the clinic, and remain confined in the CRU for up to 25 consecutive days. Exclusion Criteria: 1. History or presence of any clinically significant psychiatric, endocrine, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, renal, or other major disease or illness at Screening, which in the opinion of the Investigator would have jeopardized the safety of the patient or the validity of the study results. 2. Opioid-dependent patients who were actively seeking treatment for their moderate to severe opioid use disorder. 3. Patients with positive UDS for BPN, barbiturates, or methadone or breath alcohol on the day of check-in to the CRU. 4. Aspartate aminotransferase (AST) levels \>3 X the upper limit of normal, alanine aminotransferase (ALT) levels \>3 X the upper limit of normal, total bilirubin \>1.5 X the upper limit of normal, or creatinine \>1.5 X the upper limit of normal on the Screening laboratory assessments and at inpatient check-in, or other clinically significant laboratory abnormalities, which in the opinion of the Investigator may have prevented the patient from safely participating in study. 5. Any clinically significant abnormality on the basis of medical history, vital signs, physical examination, 12-lead electrocardiogram (\[ECG\], QTcF ≥450 msec for males or ≥470 msec for females), and laboratory evaluation (including hematology, clinical chemistry, urinalysis, and serology \[optional\]) at Screening, in the opinion of the Investigator. 6. Significant symptoms, medical conditions, or other circumstances which, in the opinion of the Investigator, would have precluded compliance with the protocol, adequate cooperation in the study or obtaining informed consent, or may have prevented the patient from safely participating in study (including, but not limited to, the risks described as precautions, warnings, and contraindications in the current version of the Investigator's Brochure for CAM2038). 7. Patients were carefully screened to exclude individuals presenting with a clinically significant history of seizure disorders, history of asthma or other respiratory disorders, head injury, hypertension, or personal history of cardiovascular disease or clinically significant ECG abnormalities. 8. Current diagnosis of Acquired Immune Deficiency Syndrome. 9. Current diagnosis of chronic pain requiring opioids for treatment. 10. Patients who met the criteria for a diagnosis of moderate or severe substance use disorder according to DSM-V criteria for any other substances other than opioids, caffeine, or tobacco. 11. Pregnant or lactating, or planned to become pregnant during the study. 12. Clinically significant history of or current evidence of suicidal ideation or active suicidal behavior as based on the Columbia-Suicide Severity Rating Scale (C-SSRS; grade 4 or 5). 13. Hypersensitivity or allergy to BPN or other opioids or excipients of CAM2038. 14. Intolerance to venipuncture and/or difficulty with venous access, as per the judgment of the Investigator/research staff. 15. Patient was using an investigational drug or monoamine oxidase inhibitor or had used such within the last 30 days (or 5 times the half-life of the drug, if known and longer) prior to first drug administration in the Qualification Phase (i.e., IR morphine sulfate). 16. Required current use of agents that were strong inhibitors or inducers of cytochrome P450 3A4 (CYP3A4), such as some azole antifungals (e.g., ketoconazole), macrolide antibiotics (e.g., clarithromycin), or protease inhibitors (e.g., ritonavir, indinavir, and saquinavir). 17. If the patient was currently on probation or had any pending legal action that could have prohibited participation or compliance in the study. 18. A patient who, in the opinion of the Investigator, was considered unsuitable or unlikely to comply with the study protocol for any reason.