Regular cannabis use in adolescence cumulatively increases the risk of subclinical psychotic symptoms, including paranoia and hallucinations, with a persisting effect after abstinence.
Summary
Adolescent cannabis use (n=1.009 boys, age 13–18) → subclinical psychosis symptoms +21% per year of use; paranoia odds +133%, hallucination odds +92% (p<0.05 each); effect still detectable after 1-year abstinence. Early onset and cumulation confirmed as risk factors.
P
PopulationMale adolescents (boys, recruited from grade 1 and grade 7), n=1.009, observation from age 13 to 18 years
I
InterventionRegular cannabis use (self-reported frequency), cumulative over adolescent years
O
OutcomePer year of regular cannabis use, increase in subclinical psychotic symptoms by 21%; increased odds for paranoia (+133%) and hallucinations (+92%); effects persisted after one year of abstinence; no evidence of reverse causation
Confidence in the evidence
Very lowLowModerateHigh
Low
The second of four GRADE levels, the effect estimate is of limited reliability.
Quality profile
Sample size★★★★★
Blinding—
Effect sizeHarm
Citations / year★★★★★
Authors
Bechtold J, Hipwell A, Lewis DA, Loeber R, Pardini D.
<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.