Five studies were included in the review (n=1.036 participants, range 43 to 518): one randomised controlled trial (n=253 participants), one quasi-randomised study (n=69 participants), and three non-randomised studies (n=714 participants). Groups were comparable at baseline in three studies. Follow-up rates ranged from 52 to 68% in the two studies with follow-up; neither used intention-to-treat analysis. The three other studies were cross-sectional and did not report participation rates; the representativeness of their samples was uncertain.
Illicit opioid use was significantly reduced in the treatment group compared to controls in all four studies reporting this outcome, with risk reductions ranging from 62 to 91%. In the fifth study, there was a statistically significant reduction over time in the number of institutional drug charges among treated participants compared with control groups.
Two of three relevant studies reported a significant reduction (55% and 75%) in injecting drug use in the opioid substitution treatment group compared with the control group; the third study reported no statistically significant difference between the groups.
Three studies reported a statistically significant reduction in needle and syringe sharing in the treatment group compared to controls, with risk reductions ranging from 47 to 73%. None of the studies reported HIV incidence.
The review reported risk ratios and 95% confidence intervals for all pre-specified outcomes for each study.