What predicts illicit drug use versus police-registered drug offending? Findings from the Finnish "From a Boy to a Man" birth cohort study.

Aims: To study whether drug offenders differ in childhood and in early adulthood from those who only report using illicit drugs.

Design: Prospective nationwide birth cohort study. Baseline survey in 1989, follow-up data collection from self-reports, police and military registers in late adolescence and early adulthood.

Participants: Two-thousand nine hundred and forty six Finnish boys born in 1981. Information about self-reported drug use at age 18 or police-registered drug offending at age 17-20 was available from 79.3% (n = 2,336) of the subjects.

Measurements: At age 8, psychopathology was assessed using the parent and teacher Rutter scales and child self-reports (Child Depression Inventory). ICD-10 psychiatric diagnoses at early adulthood according to the military register were based on a medical examination.

Findings: Childhood psychopathology did not predict self-reported drug use at age 18. Both conduct and hyperactivity problems at age 8 predicted drug offences at age 16-20. The predictive association with drug offences was strongest with severe level (over 90th percentile cut-off point) of conduct (OR 5.5, 95% CI 2.9-10.5) and hyperactivity problems (OR 5.0, 95% CI 2.7-9.3). Also moderate level of conduct (OR 2.9, 95% CI 1.7-4.9) and hyperactivity problems (OR 3.1, 95% CI 1.9-5.1) predicted drug offending. Having a psychiatric diagnosis in early adulthood associated with both self-reported use (OR 4.1, 95% CI 2.4-6.8) and drug offending (OR 13.2, 95% CI 8.3-21.2).

Conclusions: Drug offending is part of a life-course-persistent deviance, whereas for self-reporters, psychiatric problems arise later in life. Accordingly, the preventive needs, and the age period for intervention are different for boys with divergent illicit drug use involvement.