Evaluation of Buprenorphine Extended-Release Subcutaneous Injection at Alternative Injection Locations

Inclusion Criteria: 1. Signed the informed consent form (ICF) and have the ability to comply with the requirements and restrictions listed therein. 2. Sex: male or female. 3. Between the ages of 18 and 65 years inclusive, at the time of signing the ICF. 4. Currently meets Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) criteria for moderate or severe opioid use disorder (OUD), or documented history of moderate to severe OUD and receiving/stabilized on medicine for opioid use disorder (MOUD). 5. Body mass index: ≥ 18.0 to ≤ 33.0 kg/m\^2. 6. New to treatment and seeking MOUD, or currently prescribed transmucosal (TM) buprenorphine (BUP) for OUD at the dose of 12 mg daily or can dose adjust to 12 mg daily. 7. Agree not to take any BUP-containing products, other than those administered for the current study, throughout the duration of the study. Exclusion Criteria: 1. Has current diagnosis, other than OUD, requiring chronic opioid treatment. 2. Has concurrent primary substance use disorder, as defined by DSM-5 criteria, other than opioid, tobacco, cannabis, or mild to moderate alcohol use disorders. 3. Has target areas unsuitable for subcutaneous injections or evaluation of injections site (eg, nodules, scarring, lesions, excessive pigment) in the areas designated for possible injection in the study. 4. Has had significant traumatic injury or major surgical procedure (as defined by the investigator) within 30 days prior to the first dose of SUBLOCADE or still recovering from prior such injury or surgery. 5. Known personal and/or family history of congenital QT prolongation, or taking Class IA antiarrhythmic medications (eg, quinidine, procainamide, disopyramide) or Class III antiarrhythmic medications (eg, sotalol, amiodarone) or other medications that prolong the QT interval. Known family history of sudden unexplained death. 6. Currently taking (within the 30 days prior to signing the ICF) prescription or over-the-counter medications that are clinically relevant CYP 3A4 or CYP 2C8 inducers or inhibitors (eg, rifampin, azole antifungals \[eg, ketoconazole\], macrolide antibiotics \[eg, erythromycin\]). 7. Has history of suicidal ideation within 30 days prior to informed consent or history of a suicide attempt in the 6 months prior to informed consent. 8. Has any active medical condition, or psychiatric illness, or social/legal situation (including court order requiring treatment for OUD), or organ disease, or concurrent medication/treatment that may compromise participant safety, interfere with study endpoints, or limit compliance with study requirements, or compromise the ability of the participant to provide written informed consent. 9. Moderate or severe hepatic impairment (Child-Pugh B or C). 10. Has known allergy or hypersensitivity to BUP or any component of the ATRIGEL Delivery System. 11. Concurrent or has had prior treatment with any BUP long-acting injectable product (eg, SUBLOCADE) in the past 3 years prior to consent; or treatment with depot naltrexone within the 3 months prior to consent. 12. Treatment with another investigational agent within 30 days prior to Screening or enrollment in another clinical study (except for an observational study). 13. Concurrent treatment with medications contraindicated for use with BUP as per local prescribing information. 14. Is a member of site staff, has a financial interest in Indivior, or is an immediate family member of anyone directly involved in the study (ie, site staff or Indivior employee).