Nunes EV, Bisaga A, Krupitsky E, et al. - In this posthoc analysis, the temporal correlation between episodes of opioid use and subsequent dropout in a placebo-controlled trial of extended-release injection naltrexone (XR-NTX) was determined in order to describe inferences concerning the mechanism by which extended blockade of opioid receptors translates into clinical effectiveness. Researchers conducted a 24-week multiple-site, double-blind, randomized trial of monthly XR-NTX vs placebo injections at the setting of 13 addiction treatment programs in Russia, 2008–09. 250 adults with opioid use disorder who had completed in-patient detoxification were provided XR-NTX injection or placebo injection every 4 weeks with weekly clinic visits and biweekly counseling. Outcomes suggest that the risk of dropout from opioid use disorder treatment after an episode of opioid use could be reduced using the extended-release injection naltrexone. No opioid-positive urine tests were evident in just under a third of patients (31%) on XR-NTX across the trial, however, the hypothesis that this would differ from placebo (20%) was not confirmed.