Amanda E Perry, Matthew Neilson, Marrissa Martyn‐St James, Julie M Glanville, Rebecca Woodhouse, Christine Godfrey, Catherine Hewitt

This is an updated version of an original Cochrane review published in Issue 3 2006 (Perry 2006). The review represents one from a family of four reviews focusing on interventions for drug-using offenders. This specific review considers interventions aimed at reducing drug use or criminal activity, or both for drug-using offenders with co-occurring mental illness. To assess the effectiveness of interventions for drug-using offenders with co-occurring mental illness in reducing criminal activity or drug use, or both. We searched 14 electronic bibliographic databases up to May 2014 and 5 Internet resources (searched between 2004 and 11 November 2009). We contacted experts in the field for further information. We included randomised controlled trials designed to reduce, eliminate, or prevent relapse of drug use and criminal activity, or both in drug-using offenders with co-occurring mental illness. We also reported data on the cost and cost-effectiveness of interventions. We used standard methodological procedures expected by The Cochrane Collaboration. Eight trials with 2058 participants met the inclusion criteria. The methodological quality of the trials was generally difficult to rate due to a lack of clear reporting. On most 'Risk of bias' items, we rated the majority of studies as unclear. Overall, we could not statistically combine the results due to the heterogenous nature of the different study interventions and comparison groups. A narrative summary of the findings identified that the interventions reported limited success with reducing self report drug use, but did have some impact on re-incarceration rates, but not re-arrest. In the single comparisons, we found moderate-quality evidence that therapeutic communities determine a reduction in re-incarceration but reported less success for outcomes of re-arrest, moderate quality of evidence and self report drug use. Three single studies evaluating case management via a mental health drug court (very low quality of evidence), motivational interviewing and cognitive skills (low and very low quality of evidence) and interpersonal psychotherapy (very low quality of evidence) did not report significant reductions in criminal activity and self report drug use respectively. Quality of evidence for these three types of interventions was low to very low. The trials reported some cost information, but it was not sufficient to be able to evaluate the cost-effectiveness of the interventions. Two of the five trials showed some promising results for the use of therapeutic communities and aftercare, but only in relation to reducing subsequent re-incarceration. Overall, the studies showed a high degree of variation, warranting a degree of caution in the interpretation of the magnitude of effect and direction of benefit for treatment outcomes. More evaluations are required to assess the effectiveness of interventions for drug-using offenders with co-occurring mental health problems.