Pharmacokinetics, Safety, and Tolerability of Depot Buprenorphine at Three Different Molecular Weights in Treatment-Seeking Subjects With Opioid Use Disorder

Inclusion Criteria: * Currently meets DSM-5 criteria for moderate or severe opioid use disorder (OUD) * Is seeking treatment for OUD * Body mass index: ≥ 18.0 to ≤ 35.0 kg/m\^2 * Females: Female individuals of childbearing potential (defined as all women who are not surgically sterile or postmenopausal for at least 1 year prior to informed consent) must have a negative serum pregnancy test prior to enrollment and must agree to use a medically acceptable means of contraception from Screening through at least 6 months after the last dose of Investigational Medicinal Product (IMP). * Males: Male individuals with female partners of child-bearing potential must agree to use medically acceptable contraception after signing the informed consent form through at least 6 months after the last dose of IMP. Male individuals must also agree not to donate sperm during the study and for 6 months after receiving the last dose of IMP. * Have a normal electrocardiogram (ECG) or ECG with no clinically significant findings in the opinion of the Investigator or medically qualified sub-investigator at Screening and through pre-dose on Day 1. * Agree not to take any buprenorphine-containing products, other than those administered for the current study, throughout the duration of the study. * Willing to adhere to study procedures and provide written informed consent prior to start of any study procedures. Exclusion Criteria: * Current diagnosis, other than OUD, requiring chronic opioid treatment. * Pregnant or lactating females. * Have an ECG demonstrating a corrected QT interval using Fridericia's calculation (QTcF) \> 450 msec in males and QTcF \> 470 msec in females upon admission to the residential facility or prior to administration of RBP-6000. * Currently meet the criteria for diagnosis of moderate or severe substance use disorder, by DSM-5 criteria, for any substances other than opioids, and/or tobacco. * Had a significant traumatic injury, major surgery, or open biopsy within the 4 weeks prior to signing the informed consent form. * Used buprenorphine-containing products within the 14 days prior to signing the informed consent form. * Have a history of suicidal ideation within the 30 days prior to signing the informed consent form or prior to study drug administration * Have a history or presence of allergic or adverse response (including rash or anaphylaxis) to buprenorphine, naloxone, methadone, or the ATRIGEL Delivery System. * Individuals who have a positive urine drug screen (UDS) prior to admission to the residential facility for barbiturates, benzodiazepines, buprenorphine, or methadone.