The effect of entry and retention in opioid substitution therapy on contact with the criminal justice system among opioid dependent people

Background: Evidence on the effectiveness of opioid substitution therapy (OST) in reducing crime is mixed. We evaluate the effectiveness of OST in delaying time to first charge, reducing total charge-days, and examine the relationship between OST retention and total charges.

Methods: Retrospective study of 10,744 OST entrants in New South Wales, Australia, linked to data on charges, incarceration and mortality. OST exposure was modelled in a time-dependent manner using Cox proportional hazards models (time to first charge) and Anderson-Gill intensity models (total charge-days). Retention in OST was modelled as number of OST treatment episodes and proportion of follow-up in treatment using zero-inflated negative binomial regression (total number of charges). All models were adjusted for sociodemographic, criminogenic and treatment-related variables.

Results: Overall, 5,751 (53.5%) people were charged with an offence. In adjusted analyses, OST was associated with an initial benefit in delaying the time to first charge (Hazards Ratio (HR) 0.43, 95% Confidence Interval (CI) 0.33-0.55) and reducing total charge-days (HR 0.39, 95% CI 0.30-0.52), however, these protective effects decayed over time. The total charge rate was higher as the number of treatment episodes increased (Incident Rate Ratio (IRR) 1.13, 95% CI 1.11-1.15) and the proportion of follow-up spent in treatment decreased (IRR for the lowest proportion of follow-up in treatment 1.11, 95% CI 1.02-1.21).

Conclusions: OST significantly reduces overall charge rates, however, is most protective with greater treatment engagement. These findings reinforce the importance of treatment retention in order to maximise the long-term health and social benefits of OST.