A major goal for the treatment of opioid use disorder is to reduce or eliminate the use of illicit opioids. Buprenorphine, a μ-opioid receptor partial agonist and kappa opioid receptor antagonist, is now being developed as a monthly, sustained-release formulation (RBP-6000). The objective of this study was to demonstrate that RBP-6000 blocks the subjective effects and reinforcing efficacy of the μ-opioid receptor agonist hydromorphone (intramuscularly administered) in subjects with moderate or severe opioid use disorder. Subjects were first inducted and dose stabilized on sublingual buprenorphine/naloxone (8-24 mg daily; dose expressed as the buprenorphine component), then received two subcutaneous injections of RBP-6000 (300 mg) on Day 1 and Day 29. Hydromorphone challenges (6 mg, 18 mg or placebo administered in randomized order) occurred on 3 consecutive days of each study week before and after receiving RBP-6000. Subjects reported their responses to each challenge on various 100-mm Visual Analogue Scales (VAS). Subjects also completed a choice task to assess the reinforcing efficacy of each hydromorphone dose relative to money. At baseline, mean "drug liking" VAS scores for hydromorphone 18 mg and 6 mg versus placebo were 61 mm (95% confidence interval, 52.3-68.9) and 45 mm (95% confidence interval, 37.2-53.6), respectively. After 300 mg RBP-6000 was administered, mean VAS score differences from placebo were less than 10 mm through week 12. The reinforcing efficacy of hydromorphone decreased in a parallel manner. This study demonstrated that RBP-6000 at a 300 mg dose provides durable and potent blockade of the subjective effects and reinforcing efficacy of hydromorphone in subjects with moderate or severe opioid use disorder.