Capping Police Diversion: What Happens When Limits Are Placed on a Longstanding and Legislated Drug Diversion Program?

Police drug diversion programs offer alternatives to criminal punishment for possession and can reduce recidivism, costs, and harm. Eligibility criteria—such as age or offence type—are critical to program function, yet there remain ongoing debates about optimal design. This study analyses outcomes following a 2019 legislative reform that capped diversion episodes at two within four years in the South Australian Police Drug Diversion Initiative, a long-standing program internationally recognised as an exemplar of police-led drug diversion. Using interrupted time series analysis and SARIMA modelling, we examined changes in diversion rates across 22 years (2001–2023; 65,788 discrete episodes). Chi-square tests explored changes in client profiles. Before the cap, diversions increased year-on-year, driven largely by methamphetamine-related episodes. The cap's introduction coincided with an immediate 50% monthly reduction (n = 253) in April 2019 relative to the pre-intervention trend. By study end, monthly diversions were 70% (n = 24,069 fewer episodes cumulatively) lower than the counterfactual. The composition of diverted clients shifted markedly after the cap, indicating changes in who received diversion. The 2019 cap was associated with a large, sustained decline in diversion activity that exceeded expectations and altered program reach. The change in legislation coincided with thousands of individuals with minor drug charges no longer accessing health-oriented interventions and avoiding court or criminal conviction. Broader systemic shifts in policing or program delivery, limiting access even for technically eligible people, were also observed. These findings highlight the need to consider downstream and equity impacts when designing diversion eligibility rules.