A longitudinal study of 372 adolescents found that higher polygenic risk scores for schizophrenia were associated with stronger increases in cannabis use during ages 16-20, while no relationship was found for alcohol or tobacco, supporting a shared genetic basis between schizophrenia and cannabis use.
Read this if you are interested in the genetic connection between schizophrenia risk and cannabis use during adolescence.
Schizophrenia genetic risk predicted cannabis use increases specifically, not alcohol or tobacco
What the researchers found
Researchers followed 372 adolescents from the RADAR-Y study, tracking substance use from ages 13-20 while measuring each participant's genetic vulnerability to schizophrenia using polygenic risk scores.
High schizophrenia genetic vulnerability was specifically associated with a stronger increase in cannabis use during ages 16-20. This relationship was consistent across multiple polygenic risk score thresholds.
No clear relationship was found between schizophrenia genetic risk and smoking or alcohol use, making the association specific to cannabis.
This specificity is particularly noteworthy: if the association were simply about genetic predisposition to substance use in general, it should have appeared for alcohol and tobacco as well. The cannabis-specific finding supports the hypothesis that shared genetic factors specifically link schizophrenia vulnerability and cannabis use behavior.
Why it matters
This finding helps explain why cannabis use and schizophrenia co-occur: it may not be simply that cannabis causes psychosis, but that shared genetic factors make some individuals both more likely to use cannabis and more vulnerable to schizophrenia. This has profound implications for understanding causation in the cannabis-psychosis relationship.
The numbers in context
372 adolescents followed ages 13-20. Higher schizophrenia PRS predicted stronger cannabis use increase ages 16-20 (multiple thresholds significant at p<0.001). No relationship with alcohol or smoking. Cannabis-specific association supports shared genetic architecture.
How the study worked
Longitudinal cohort (RADAR-Y study, N=372). Piecewise latent growth curve modeling analyzed cannabis, smoking, and alcohol use trajectories from ages 13-20 (split at age 16). Polygenic risk scores for schizophrenia calculated at multiple p-value thresholds. Bonferroni-corrected significance at p<0.001.
What this study cannot tell us
Moderate sample size (372) for genomic analyses. Dutch adolescent sample may not generalize to other populations. Polygenic risk scores explain only a small fraction of schizophrenia heritability. Cannabis use was self-reported. The study period (ages 13-20) may miss later-onset patterns.
How to read the evidence
Longitudinal cohort with genomic data and rigorous statistical correction provides moderate evidence on the genetic overlap between schizophrenia vulnerability and cannabis use patterns.
When this study was published
Published in 2018. Larger genome-wide studies have since expanded understanding of the genetic overlap between cannabis use and psychiatric disorders.
The bigger picture
This study adds to growing evidence that the cannabis-schizophrenia association is partly driven by shared genetics rather than a simple one-way causal path. Individuals with higher genetic loading for schizophrenia may be drawn to cannabis for reasons related to their neurobiology, creating a complex interplay between genetic vulnerability, cannabis use, and psychosis risk.
Questions still open
- Do adolescents with high schizophrenia PRS self-medicate with cannabis for prodromal symptoms? Would cannabis prevention in genetically high-risk adolescents reduce psychosis onset? Are there specific genetic variants that drive both cannabis preference and schizophrenia risk?
Common questions
Is the link between cannabis and schizophrenia genetic?
Did the genetic risk affect use of other substances?
Read the original research
Genetic vulnerability to schizophrenia is associated with cannabis use patterns during adolescence.
Drug and alcohol dependence, 190, 143-150
Citation
Hiemstra, Marieke; Nelemans, Stefanie A; Branje, Susan; van Eijk, Kristel R; Hottenga, Jouke-Jan; Vinkers, Christiaan H; van Lier, Pol; Meeus, Wim; Boks, Marco P. (2018). Genetic vulnerability to schizophrenia is associated with cannabis use patterns during adolescence.. Drug and alcohol dependence, 190, 143-150. https://doi.org/10.1016/j.drugalcdep.2018.05.024
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