A GWAS of lifetime cannabis use (184 765 total sample size, 43 380 cases) identified eight genome-wide significant loci and 35 significant genes.5 Twin studies suggest high genetic correlations between early stages of cannabis experimentation and later cannabis use disorder.6 However, casual cannabis use is affected by a variety of socioenvironmental influences and age-period-cohort effects, whereas progression to cannabis use disorder is related to other psychopathologies. Findings have suggested partially distinct genetic causes underlying alcohol consumption and alcohol use disorder, including different genetic associations with other psychiatric disorders and traits.7, 8 Thus, in addition to examining the genomic liability for cannabis use disorder, we tested whether the genetic influences underlying cannabis use and cannabis use disorder diverge with respect to behavioural and brain measures.
