Concurrent and Sustained Cumulative Effects of Adolescent Cannabis Use on Subclinical Psychotic Symptoms.

<h4>Objective</h4>Adolescents who regularly use Cannabis may be at heightened risk of developing subclinical and clinical psychotic symptoms. However, this association could be explained by reverse causation or other factors. To address these limitations, the current study examined whether adolescents who engage in regular Cannabis use exhibit a systematic increase in subclinical psychotic symptoms that persists during periods of sustained abstinence.<h4>Method</h4>The sample comprised 1,009 boys who were recruited in 1st and 7th grades. Self-reported frequency of Cannabis use, subclinical psychotic symptoms, and several time-varying confounds (e.g., other substance use, internalizing/externalizing problems) were recorded annually from age 13 to 18. Fixed-effects (within-individual change) models examined whether adolescents exhibited an increase in their subclinical psychotic symptoms as a function of their recent and/or cumulative history of regular Cannabis use and whether these effects were sustained following abstinence. Models controlled for all time-stable factors (default) and several time-varying covariates as potential confounds.<h4>Results</h4>For each year adolescent boys engaged in regular Cannabis use, their expected level of subsequent subclinical psychotic symptoms rose by 21% and their expected odds of experiencing subsequent subclinical paranoia or hallucinations rose by 133% and 92%, respectively. The effect of prior regular Cannabis use on subsequent subclinical psychotic symptoms persisted even when adolescents stopped using Cannabis for a year. These effects were after controlling for all time-stable and several time-varying confounds. No support was found for reverse causation.<h4>Conclusions</h4>These results suggest that regular Cannabis use may significantly increase the risk that an adolescent will experience persistent subclinical psychotic symptoms.