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AIM: To examine the associations between frequency of cannabis use and psychosocial outcomes in adolescence/young adulthood. DESIGN: A 21-year longitudinal study of the health, development and adjustment of a birth cohort of 1265 New Zealand children. MEASUREMENTS: Annual assessments of the frequency of cannabis use were obtained for the period from age 14-21 years, together with measures of psychosocial outcomes including property/violent crime, depression, suicidal ideation, suicide attempt and other illicit drug use. FINDINGS: The frequency of cannabis use was associated significantly with all outcomes, and particularly other illicit drug use. Statistical control for confounding by both fixed and time-dynamic factors substantially reduced the strength of association between cannabis use and outcome measures. Nevertheless, cannabis use remained significantly (P < 0.05) associated with all outcomes and particularly other illicit drug use, after adjustment for confounding. For the measures of crime, suicidal behaviours and other illicit drug use there was evidence of age related variation in the strength of association with cannabis use, with younger (14-15 years old) users being more affected by regular cannabis use than older (20-21 years old) regular users. However, the association between cannabis use and depression did not vary with age. CONCLUSIONS: Cannabis use, and particularly regular or heavy use, was associated with increased rates of a range of adjustment problems in adolescence/ young adulthood-other illicit drug use, crime, depression and suicidal behaviours-with these adverse effects being most evident for school-aged regular users. The findings reinforce public health concerns about minimizing the use of cannabis among school-aged populations.
Fergusson et al. (Fri,) studied this question.