BACKGROUND: The review represents one in a family of four reviews focusing on a range of different interventions for drug-using offenders. This specific review considers pharmacological interventions aimed at reducing drug use and/or criminal activity for illicit drug-using offenders. OBJECTIVES: To assess the effectiveness of pharmacological interventions for drug-using offenders in reducing criminal activity and/or drug use. SEARCH METHODS: Fourteen electronic bibliographic databases (searched between 2004 and 21 March 2013) and five additional Web resources (searched between 2004 and 11 November 2011) were searched. Experts in the field were contacted for further information. SELECTION CRITERIA: Randomised controlled trials assessing the efficacy of any pharmacological interventions for reducing, eliminating or preventing relapse in drug-using offenders were included. Data on the cost and cost-effectiveness of interventions were reported. DATA COLLECTION AND ANALYSIS: We used standard methodological procedures as expected by The Cochrane Collaboration. MAIN RESULTS: A total of 76 trials across the four reviews were identified. After a process of prescreening had been completed, 17 trials were judged to meet the inclusion criteria for this specific review (six of the 17 trials are awaiting classification for the review). The remaining 11 trials contained a total of 2,678 participants. Nine of the eleven studies used samples with a majority of men. The interventions (buprenorphine, methadone and naltrexone) were compared to non pharmacological treatments (e.g., counselling) and other pharmacological drugs. The methodological trial quality was poorly described, and most studies were rated as 'unclear' by the reviewers. The biggest threats to risk of bias were generated through blinding (performance and detection bias) and incomplete outcome data (attrition bias). When combined, the results suggest that pharmacological interventions do significantly reduce subsequent drug use using biological measures, (three studies, 300 participants, RR 0.71 (95% CI 0.52 to 0.97)), self report dichotomous data (three studies, 317 participants, RR 0.42, (95% CI 0.22 to 0.81)) and continuous measures (one study, MD -59.66 (95% CI -120.60 to 1.28)) . In the subgroups analysis for community setting, (two studies, 99 participants: RR 0.62 (95% CI 0.35 to 1.09)) and for secure establishment setting, (one study, 201 participants: RR 0.76 (95% CI 0.52 to 1.10)), the results are no longer statistically significant. Criminal activity was significantly reduced favouring the dichotomous measures of re arrest, (one study, 62 participants, RR 0.60 (95% CI 0.32 to 1.14)), re-incarceration, (three studies, 142 participants, RR 0.33 (95% CI 0.19 to 0.56)) and continuous measures (one study, 51 participants, MD -74.21 (95% CI -133.53 to -14.89)). Findings on the effects of individual pharmacological interventions on drug use and criminal activity show mixed results. Buprenorphine in comparison to a non pharmacological treatment seemed to favour buprenorphine but not significantly with self report drug use, (one study, 36 participants, RR 0.58 (95% CI 0.25 to 1.35)). Methadone and cognitive behavioural skills in comparison to standard psychiatric services, did show a significant reduction for self report dichotomous drug use (one study, 253 participants, RR 0.43 (95% CI 0.33 to 0.56)) but not for self report continuous data (one study 51 participants) MD -0.52 (95% CI -1.09 to 0.05)), or re incarceration RR 1.23 (95% CI 0.53 to 2.87)). Naltrexone was favoured significantly over routine parole and probation for re incarceration (two studies 114 participants, RR 0.36 (95% CI 0.19 to 0.69)) but no data was available on drug use. Finally, we compared each pharmacological treatment to another. In each case we compared methadone to: buprenorphine, diamorphine and naltrexone. No significant differences were displayed for either treatment for self report dichotomous drug use (one study, 193 participants RR 1.23 (95% CI 0.86 to 1.76)), continuous measures of drug use MD 0.70 (95% CI -5.33 to 6.73) or criminal activity RR 1.25 (95% CI 0.83 to 1.88)) between methadone and buprenorphine. Similiar results were found for comparisons with Diamorphine with no significant differences between the drugs for self report dichotomous drug use for arrest (one study, 825 participants RR 1.25 (95% CI 1.03-1.51)) or Naltrexone for dichotomous measures of re incarceration (one study, 44 participants, RR 1.10 (95% CI 0.37 to 3.26)), and continuous outcome measure of crime MD -0.50 (95% CI -8.04 to 7.04)) or self report drug use MD 4.60 (95% CI -3.54 to 12.74)). AUTHORS' CONCLUSIONS: Pharmacological interventions for drug-using offenders do appear to reduce overall subsequent drug use and criminal activity (but to a lesser extent). No statistically significant differences were displayed by treatment setting. Individual differences are displayed between the three pharmacological interventions (buprenorphine, methadone and naltrexone) when compared to a non pharmacological intervention, but not when compared to each other. Caution should be taken when interpreting these findings, as the conclusions are based on a small number of trials, and generalisation of these study findings should be limited mainly to male adult offenders. Additionally, many studies were rated at high risk of bias because trial information was inadequately described.