The issue is further complicated by tentative evidence for interactions between cannabis use and genetic risk variants for schizophrenia24. Schizophrenia is known to be highly heritable with up to 80% of the variance explained by additive genetic effects25, and as sample sizes have increased a growing number of genetic risk variants have been identified26, 27. Interactions between risk variants and cannabis use might explain why some individuals experience psychosis while others do not. However, cannabis use itself has been reported to be heritable28–30, though no genetic risk variants have been identified31. It is unclear to what extent the heritability of cannabis use results from shared heritability with other behavioural phenotypes such as schizophrenia predicting its use.
