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Background: In Sweden, as in other countries, individuals with immigrant backgrounds are disproportionately represented within the incarcerated population. This study examined the association between immigrant background and future incarceration for individuals assessed for illicit substance use severity, while considering their prior incarceration history.

Methods: Using data from Swedish Addiction Severity Index (ASI) assessments linked to register data from Statistics Sweden, we employed Zero-Inflated Negative Binomial (ZINB) regression models to analyse differences in incarceration histories within five years before and after ASI assessments based on immigrant backgrounds. Additionally, Cox proportional-hazard models were used to assess the likelihood of post-assessment incarceration among these groups.

Results: Immigrant background was positively associated with pre- and post-assessment incarceration. First- and second-generation immigrants from the Global South had longer periods of incarceration in the five years before assessments compared to native Swedes. Post-assessment, first-generation immigrants showed longer periods of incarceration. Survival analyses supported these findings, indicating a higher risk of prolonged post-assessment incarceration among all immigrant groups, particularly first-generation immigrants from the Global South.

Conclusion: Among individuals assessed for illicit drug use within Swedish municipalities, those with immigrant backgrounds faced higher incarceration risks, even after controlling for substance use severity and prior incarceration. Tailored interventions and support systems are vital to prevent re-entry into the criminal justice system. Timely actions can break re-offending cycles, redirecting paths away from reoffending and towards legal reintegration, thereby reducing incarceration and recidivism rates.