Under the best-fitting model (shown in Table 4), heritable influences accounted for over 60% of the variance in alcohol consumption, cannabis use, and cannabis dependence symptoms (61.0%, 67.1%, and 72.2%, respectively). The heritability estimate was lowest – but still quite substantial – for AD symptoms: 46.8% of variance could be attributed to genetic factors. As noted above, we did not find evidence that shared environmental factors exert a significant influence on use or dependence symptomatology for alcohol or cannabis.
