The heritability of cannabis exposure (ever vs. never used) was estimated at 67.2% (standard error=13.6%, p<0.001; Table 3). All brain volumes of interest were also significantly heritable. There was no evidence for contributions of shared rearing environment. As above, only the left amygdala (ρp=−0.175,p=0.005) and right VS (ρp=−0.154,p=0.015) showed significant phenotypic correlations with cannabis use. Decomposing these correlations, we found a significant genetic correlation between left amygdala volume and cannabis use (ρg=−0.433,p=0.004), but not a significant environmental correlation (ρe=0.280,p=0.189). Neither ρg nor ρe was significant for right VS volume.
