Inclusion Criteria:  Be between 19 and 64 years of age; Be diagnosed with moderate or severe OUD as per DSM-5 criteria; Be at high-risk for recurrent overdose, defined as having experienced a recent non-fatal overdose within the past 6 months (e.g., admission to the emergency department for an overdose OR self-reported overdose that was managed at an overdose prevention or supervised consumption site OR had an overdose where an ambulance arrived at the scene) Be interested in receiving OAT;  If assigned female sex at birth:  Be of non-childbearing potential, defined as (i) self-reported postmenopausal status (12 months of spontaneous amenorrhea and ≥ 45 years of age); or (ii) documented surgical sterilization (i.e. tubal ligation, hysterectomy, or bilateral oophorectomy); or If of childbearing potential, be willing to use an acceptable method of contraception throughout the study and have a negative pregnancy test at screening and before each drug administration; Be able and willing to follow study procedures; Be able to provide adequate locator information (e.g phone number and at least 1 emergency contact); Be able and willing to provide written informed consent, and must have provided this consent; Be able to understand, communicate and speak English.  Additional Inclusion Criteria at Day 0 (Baseline):  In addition, participants must meet ALL the following criteria at Day 0 (Visit 2) to be eligible to initiate extended-release injectable buprenorphine:  Be in adequate control of opioid withdrawal symptoms and cravings, as per investigator judgment; Be on daily buprenorphine/naloxone sublingual dose of between 8 and 24 mg for a minimum of 7 and a maximum of 28 days prior to the first XR-BUP injection.  Exclusion Criteria:  Any disabling, severe, or unstable medical or psychiatric condition that, in the opinion of the investigator, 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; Any severe or unstable co-morbid substance use disorder that, in the opinion of the investigator, precludes safe participation in the study (e.g., alcohol use disorder or benzodiazepine use disorder); Any severe hepatic impairment as demonstrated by the medical history and/or recent laboratory test results (i.e. ALT, AST) performed within the 30 days prior to baseline; History of Long QT Syndrome or an immediate family member with this condition; Be on OAT other than buprenorphine/naloxone in the 7 days prior to screening; Be on a stable buprenorphine/naloxone dose for more than 27 days prior to screening; Pregnant, breastfeeding, or planning to become pregnant during the study period; History of a serious adverse drug reaction, hypersensitivity reaction, or allergy to buprenorphine; Use of an investigational drug in the 30 days prior to screening; Incarcerated, pending legal action or other reasons that might prevent completion of the study; Current or anticipated need for treatment with any medication that may interact with buprenorphine (e.g., central nervous system depressants, cytochrome P-450 3A4 inhibitors or inducers, Class IA, Class IC, or Class III antiarrhythmic medications) and that, in the opinion of the investigator, would be deemed unsafe or could prevent study completion.