Slow-Release Oral Morphine for the Treatment of Opioid Use Disorder

Inclusion Criteria: Participants must meet all the following criteria to be eligible for the study: 1. Be between 19 and 65 years of age, inclusively; 2. Be diagnosed with opioid use disorder requiring opioid agonist treatment (OAT), as per DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition) criteria and the discretion of the study physician; 3. Be interested in receiving OAT; 4. Be willing and eligible to be randomized to slow release oral morphine (SROM) or methadone-based OAT as per British Columbia guidelines; 5. If female: 1. Be of non-childbearing potential, defined as (i) postmenopausal (12 months of spontaneous amenorrhea and over 45 years of age); or (ii) documented surgical sterilization (i.e., tubal ligation, hysterectomy, or bilateral oophorectomy); or 2. If of childbearing potential, be willing to use an acceptable method of contraception throughout the study and have a negative pregnancy test at screening; 6. Be able to provide written informed consent; 7. Be willing to comply with study procedures; 8. Be able to communicate in English; Exclusion Criteria: Participants will be excluded from the study if any of the following criteria are met: 1. Any disabling, severe, or unstable medical or psychiatric condition that, in the opinion of the study physician, precludes safe participation in the study or the ability to provide fully informed consent, as assessed by medical and psychiatric history, physical examination, vital signs, and/or laboratory tests. These may include but are not limited to: significant respiratory depression, severe respiratory compromise or obstructive disease, severe respiratory distress, acute or severe bronchial asthma, known or suspected paralytic ileus; 2. Any severe or unstable co-morbid substance use disorder (e.g., delirium tremens, acute alcohol intoxication) that, in the opinion of the study physician, precludes safe participation in the study; 3. Maintenance on buprenorphine at doses of ≥4 mg in the 5 days prior to screening and stable in the opinion of the study physician; 4. Maintenance on methadone at doses of ≥60 mg in the 5 days prior to screening and stable in the opinion of the study physician; 5. Maintenance on slow release oral morphine at doses of ≥250 mg in the 5 days prior to screening and stable in the opinion of the study physician; 6. Pregnant, breastfeeding, or planning to become pregnant during the study period; 7. History of a serious adverse drug reaction, hypersensitivity reaction, or allergy to methadone or SROM; 8. Use of an investigational drug in the 30 days prior to screening; 9. Pending legal action or other reasons that might prevent completion of the study; 10. Current or anticipated need for treatment with any medication that may interact with methadone or SROM (e.g., benzodiazepines, monoamine oxidase inhibitors \[MAOIs\] pRESTO Protocol Version 3.0, 08 October 2019 Page 21 of 66 used currently or within the past 14 days) and that, in the opinion of the study physician, would be deemed unsafe or could prevent study completion.