Here we test for such genetic overlap directly, and aim to discern the direction of causation between cannabis use and schizophrenia. Within a sample of 2,082 healthy individuals, we tested to see if polygenic risk profiles for schizophrenia predict cannabis use. Polygenic risk profiles reflect the cumulative burden of risk alleles carried by an individual as identified in a previous genome-wide association study (GWAS)32, here of 13,833 schizophrenia cases and 18,310 controls27. Such an association with cannabis use would suggest that those genetically predisposed to schizophrenia use cannabis more frequently. This would mean that the association between schizophrenia and cannabis use is not simply one of an environmental risk factor, but rather involves gene-environment correlation as individuals choose and shape their own environment based on their own innate preferences.
