Marijuana use in adolescents linked to psychotic behavior
Previous studies have linked marijuana use to the development of psychotic behavior; however, a new study has reported the opposite: psychotic behavior in adolescents is associated with the later development of marijuana use. Researchers affiliated with Leiden University in The Netherlands published their findings in the December issue of the journal Addiction.
Lead author Merel Griffith-Lendering, a doctoral candidate at the university, and colleagues designed a study to examine the direction of the longitudinal association between vulnerability for psychosis and cannabis use throughout adolescence. They studied vulnerability for the development of psychosis and cannabis use over time, while controlling for gender, family psychopathology, alcohol, use and tobacco use. The researchers accessed data from a large prospective population study of Dutch adolescents: the TRacking Adolescents′ Individual Lives Survey (TRAILS) study. The study group comprised 2,120 adolescents with assessments at (average) age 13.6, age 16.3 and age 19.1.
Vulnerability for psychosis at the three assessment points was represented by latent (dormant) factors derived from scores on three scales of the Youth Self Report and the Adult Self Report, i.e. Thought Problems, Social Problems and Attention Problems. Participants self- reported on cannabis use during the past year at all three waves.
The researchers found significant associations between psychosis vulnerability and cannabis use at all assessments. In addition, cannabis use at age 16 predicted psychosis vulnerability at age 19. Furthermore, psychosis vulnerability at ages 13 predicted cannabis use at age 16 and psychosis vulnerability at age 16 predicted cannabis use at age 19.
The authors concluded that cannabis use predicts psychosis vulnerability in adolescents, and vice-versa; this finding suggests that there is a bi-directional causal association between the two. The authors noted that their study cannot prove one causes the other. Genetics may also explain the link between marijuana use and psychosis.
Another study published by Australian researchers published online in the same journal last October studied whether cannabis use in adolescence can increase the risk of developing common mental disorders. They noted that most reports have focused on associations in adolescence, with few studies extending into adulthood. Therefore, they examined the association from adolescence until the age of 29 years in a representative prospective cohort of young Australians.
The investigators noted that they designed a nine-wave, 15-year representative longitudinal cohort study, with six waves of data collection in adolescence (average age 14.9–17.4 years) and three in young adulthood (average age 20.7, 24.1 and 29.1 years). The study group comprised 1,943 individuals recruited in secondary school and surveyed at each wave when possible from mid-teen age to their late 20s.
Psychiatric behavior was assessed with the Revised Clinical Interview Schedule (CIS-R) at each adolescent wave, and as Composite International Diagnostic Interview (CIDI)-defined ICD-10 major depressive episode and anxiety disorder at 29 years. Frequency of cannabis use was measured in the past six months in adolescence. Cannabis use frequency in the last year and DSM-IV cannabis dependence were assessed at 29 years. Cross-sectional and prospective associations of these outcomes with cannabis use and dependence were estimated as odds ratios (OR), using multivariable logistic regression models, with the outcomes of interest, major depressive episode (MDE) and anxiety disorder (AD) at 29 years.
The researchers found no consistent associations between adolescent cannabis use and depression at age 29 years. However, daily cannabis use was associated with anxiety disorder at 29 years, as was cannabis dependence (adjusted OR 2.2, 95% CI: 1.1–4.4). Among weekly adolescent cannabis users, those who continued to use cannabis use daily at 29 years remained at significantly increased odds of anxiety disorder.
The authors concluded that regular (particularly daily) adolescent cannabis use is associated consistently with anxiety, but not depressive disorder, in adolescence and late young adulthood, even among regular users who then cease using the drug. They suggested that it was possible that early cannabis exposure causes enduring mental health risks in the general cannabis-using adolescent population.