Early Cannabis Use Strongly Predicts Arrest and Incarceration by Age 18

Early-onset cannabis use strongly predicted lifetime arrest (p = 0.013), probation (p = 0.034), and incarceration (p = 0.093) by age 18. After adjusting for comorbid mental disorders and family-level unobserved factors using sibling comparisons, ADHD, ODD, and anxiety/depression were not independently associated with criminal justice contact. Only conduct disorder modestly predicted victimization. Effects were mostly driven by boys.

Longitudinal study of 721 sibling pairs from the Panel Study of Income Dynamics, followed from 1997-2019. Used sibling fixed-effects models to control for shared family environment and genetic factors. Child mental health measured by the Behavior Problems Index (ages 4-12); delinquency measured by self-reported justice system contact by age 18.

By using sibling comparisons, this study controls for family environment and shared genetics that typically confound the link between substance use and delinquency. The finding that cannabis use outpredicts childhood mental disorders for justice contact is striking.

This study complicates the narrative that delinquency is primarily driven by mental health disorders. Within the same family, the sibling who started cannabis early was significantly more likely to end up in the justice system, regardless of childhood mental health status.

Mother-reported mental health measures. No information on treatment for mental disorders (especially ADHD medication). Self-reported justice contact. Cannot fully disentangle whether cannabis causes delinquency or both reflect unmeasured risk factors. Partial genetic control via sibling design.