| Summary: | Abstract The aim of this study was to investigate the association between adolescent substance use and psychosis in later life, after taking into account a wide range of known confounders, using data from the Northern Finland Birth Cohort 1986 (N = 9432). Adolescence is a vulnerable neurodevelopmental period, during which many brain maturation processes take place. Substance use during this critical period may disrupt these processes, ultimately leading to mental health problems. Several meta-analyses have demonstrated associations between cannabis use and tobacco smoking and increased risk of psychotic disorders. However, lack of data on the temporal order of the association and uncertainty in relation to the role of confounding factors warranted further studies. Furthermore, there are no longitudinal studies on the association between adolescent inhalant use and psychotic disorders. The study sample consisted of the Northern Finland Birth Cohort 1986. There were 7344 adolescents who participated in the follow-up study in 2001–2002, when they were aged 15–16 years. Adolescents who answered the questions on substance use and psychotic experiences (PROD-screen) were included in the present study. The final sample included 6542 subjects. In this study, an increased risk of psychosis was found in those subjects who had used cannabis five times or more, smoked 10 or more cigarettes daily or had used inhalants 2–4 times or more. Each of these substances were associated with psychosis in a dose-response manner, even after adjustments for confounders. In addition, initiation of daily smoking at 13 years of age or earlier was associated with increased risk of psychosis compared to later initiation. In this comprehensive longitudinal population-based study, frequent cannabis use, daily tobacco smoking and frequent inhalant use in adolescence were independently associated with increased risk of incident psychosis, even after adjusting for confounders such as baseline psychotic experiences, other substance use and history ...
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