Efficacy of maintenance treatment with methadone for opioid dependence: a meta-analytical study

The two aims of this study were to analyse the impact of methadone on outcome, and to confirm the results from previous meta-analyses by using a different methodology. The literature on randomized controlled trials (RCT) of methadone as maintenance treatment for opioid dependence was systematically reviewed. Eight studies involving 1511 patients were included. Both dichotomous and continuous variables were transformed into the standardized effect size (d). Homogeneity was analysed. A random effect model was used in all calculations. The combined analyses for retention, abuse and criminality were all significant: d=0.90, d=0.61, and d=0.35, respectively. A test of heterogeneity was significant for all three outcomes: P<0.01 for all comparisons. The type of study design was a significant moderator in five of nine comparisons: for retention in all three comparisons, concerning abuse in gradual detoxification vs. untreated controls and concerning criminality in placebo vs. untreated controls. In these sub-groups, three of six studies were homogeneous. In one study, methadone maintenance treatment reduced abuse of illegal opioids in prisoners. We conclude that methadone maintenance treatment in opioid dependence shows positive effects on retention, opioid abuse and criminality compared with non-active controlled conditions. Type of study design could explain some of the heterogeneity found. A different meta-analytical approach made it possible to confirm effects of methadone on retention and opioid abuse from previous studies and document effect on criminality.