The risk of lifetime cannabis use, defined as any use of cannabis during the lifetime, varies between individuals. Previous studies have shown that individual differences in lifetime cannabis use can be partly explained by genetic differences between individuals; a meta-analysis of twin studies reported significant heritability estimates of lifetime cannabis use of 48% for males and 40% for females.12 Shared environmental factors, such as cannabis availability and parental monitoring,13, 14 also have a role accounting for 25 and 39% of the risk for males and females, respectively.12 Also, there is substantial overlap in the genetic risks underlying lifetime cannabis use and cannabis use disorder.15
