Aims: To determine the efficacy of naltrexone in reducing illicit opioid use and the potential moderating role of treatment retention.
Design: First, randomized controlled trials (RCTs) comparing the regimens of treatment using the opioid antagonist, naltrexone, with controls were analysed by meta-analysis for treatment effect with regard to a range of outcome criteria. The degree of heterogeneity was also determined. The moderating effect of other interventions during naltrexone maintenance was then estimated, particularly with regard to their effect on treatment retention.
Participants: Fifteen studies involving 1,071 patients were found.
Measurements: All available outcomes were analysed in 10 studies of naltrexone versus control (seven placebo) and six studies of randomized psychosocial/psychopharmacological interventions.
Findings: Significant heterogeneity was found in the efficacy of naltrexone. Level of retention in treatment was found to be a moderator, explaining most of the heterogeneity found. Overall, naltrexone was significantly better than control conditions in reducing the number of opioid-positive urines. This effect was only present in the high retention subgroup for differences in retention. Contingency management (CM) increased retention and naltrexone use, resulting in a reduced number of opioid-positive urines.
Conclusion: Retention is important to the effect of naltrexone in treating opioid dependence. Contingency management is a promising method of increasing retention.