Vulnerability for psychosis at ages 13 and 16 predicts cannabis use at ages 16 and 19, and cannabis use at age 16 predicts psychosis vulnerability at age 19

Question: What is the temporal relationship between cannabis use and psychosis vulnerability in adolescents?

People: A total of 2120 Dutch adolescents born between 10 January 1989 and 30 September 1991 living in five municipalities in the north of the Netherlands. All participants were enrolled in the Tracking Adolescents’ Individual Lives Survey (TRIALS) study. Participants were interviewed at four time points: T1 mean participant age 11.1 years, T2 mean age 13.6 years, T3 mean age 16.3 years and T4 mean age 19.1 years.

Setting: The Netherlands; study years not reported.

Risk factors: Self-reported cannabis use, as assessed by response to the question ‘How often have you used cannabis in you life/in the last year?’ Answers were grouped into four categories: no use; one to two times; three to six times; and seven or more times during the past year. Assessments took place in three waves at T2, T3 and T4.

Outcomes: Psychosis vulnerability assessed using the thought, social and attention problem subscales of the youth self-report (used at T2 and T3 assessments) and the adult self-report (used at T4 assessment). Correlation between cannabis use and psychosis vulnerability across all three time points was first assessed using confirmatory factor analysis. Path analysis was then used to evaluate the temporal order cannabis use and psychosis vulnerability; the model included gender, familial psychopathology, monthly alcohol use and weekly tobacco use as covariates. Gender and family externalising disorder (family history of substance use and antisocial behaviour) were assessed at T1, and alcohol and tobacco use were assessed at T2, T3 and T4.