The effect of entry and retention in opioid agonist treatment on contact with the criminal justice system among opioid-dependent people: a retrospective cohort study

Background: Evidence on the effectiveness of opioid agonist treatment (OAT) in reducing crime is mixed. We evaluated the impact of OAT on crime in terms of delaying time to first charge and reducing overall charge rates, as well as the relationship between OAT retention and overall charge rates.

Methods: Retrospective cohort study of 10,744 new OAT entrants between 2004-2010 in New South Wales, Australia, linked to data on charges, incarceration and mortality to the end of 2011. Time-dependent OAT exposure was modelled using Cox proportional hazards models (time to first charge) and Anderson-Gill intensity models (total charge-days). Retention in OAT was modelled using two features of treatment engagement - number of OAT episodes and proportion of follow-up in OAT (presented in quartile groupings: lowest, low-mid, low-high, highest) using zero-inflated negative binomial regression (total charges). All models were adjusted for sociodemographic, criminographic and treatment-related variables.

Findings: Overall, 5,751 (53.5%) people were charged with an offence. In adjusted analyses, OAT was associated with an initial benefit in delaying the time to first charge (Hazard 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. Total charge rates were higher as the number of OAT episodes increased (Incident Rate Ratio (IRR) 1.13, 95% CI 1.11-1.15), and where relatively lower proportions of time were spent in OAT [IRR among lowest three quartiles ranged from 1.11 (95% CI 1.02-1.21) to 1.22 (95% CI 1.121-1.33)].

Interpretation: OAT is associated with a significant reduction in overall charge rates and is more protective as treatment engagement increases. Maximising treatment retention is critical to achieving long-term health and social benefits of OAT.