A longitudinal study of cannabis use and mental health from adolescence toearly adulthood

Aims. To examine the longitudinal association between cannabis use and ment al health. Design. Information concerning cannabis use and mental health fr om 15 to 21 years was available for a large sample of individuals as pan of a longitudinal study from childhood to adulthood Participants. Participant s were enrolled in the Dunedin Multidisciplinary Health and Development Stu dy, a research programme on the health, development and behaviour of a larg e group of New Zealanders born between I April 1972 and 31 March 1973. Meas urements. Cannabis use and identification of mental disorder was based upon self-report as pan of a general assessment of mental health using a standa rd diagnostic interview. Daily smoking and alcohol use at age 15 were asses sed by self-report. Indices of family socio-economic status, family climate and parent-child interaction were formed using information gathered from p arent report and behavioural observations over early childhood. Childhood b ehaviour problems were assessed by parent and reacher report. Attachment to parents was assessed in adolescence. Findings. Cross-sectional association s between cannabis use and mental disorder were significant at all three ag es. Both outcome variables shared similar pathways of low socio-economic st atus and history of behaviour problems in childhood, and low parental attac hment in adolescence. Mental disorder at age 15 led to a small but signific antly elevated risk of cannabis use at age 18; by contrast, cannabis use at age 18 elevated the risk of mental disorder at age 21. The latter associat ion reflected the extent to which cannabis dependence and other externalizi ng disorders at age 21 were predicted by earlier level of involvement with cannabis. Conclusions. The findings suggest that the primary causal directi on leads from mental disorder to cannabis use among adolescents and the rev erse in early adulthood. Both alcohol use and cigarette smoking had indepen dent associations with later mental health disorder.