Background: Among people who inject drugs, evidence suggests that contact with the criminal justice system is associated with an elevated risk of experiencing drug-related harms. Decriminalisation of drug possession and use is proposed as a response to reduce the burden of drug-related harms; however, some are concerned that removing criminal sanctions for drug possession and use will encourage increased injecting frequency and related harms.
Objective: To estimate the effect of arrest for drug possession or use (drug-related arrests; excludes cultivation and trafficking-related offences) on frequency of injecting drug use among people who inject drugs.
Methods: We will use inverse-probability weighting to estimate the average causal effect of drug-related arrests (‘intervention’) on the frequency of injecting drug use. Participants are individuals in the prospective SuperMIX cohort study who complete at least one follow up interview (N=997; observations= 4876; incident drug-related arrests=399; 2008-2023). Longitudinal causal analysis will account for pre-specified confounders (e.g. age, sex, ethnicity, income, housing, public vs private injecting location, previous IDU frequency, participation in acquisitive crime, opioid agonist treatment).
Implications: Findings will provide crucial evidence of the effect of law enforcement on deterring injecting drug use and inform debate around decriminalisation of drug possession and use. Further, findings would inform estimation of population-level changes in rates of injecting-related sequalae including overdose, injuries, and infections, and rates of emergency healthcare use if drug decriminalisation were implemented.