The SNP-heritability (h2SNP) for cannabis use disorder was 0·067–0·121 (SE 0·006–0·011) on the liability scale, depending on the estimated population prevalence and h2SNP0·02 (SE 0·002) on the raw scale. Cannabis use disorder showed significant rg with 16 of the 23 studied phenotypes, for which the strongest relationships were observed with smoking initiation36 (rg 0·66, p=3·20 × 10−83), Townsend Deprivation Index (a measure of regional poverty46; rg0·58, p=3·30 × 10−37), educational attainment47 (rg–0·39, p=6·70 × 10−34), and age at which first child is born (rg–0·49; p=5·40 × 10−28; figure 2, appendix p 18). Thus, increased risk of cannabis use disorder is genetically correlated with increased liability for smoking initiation, living in an area of high material poverty, having children at an early age, and low levels of educational attainment. Liability to cannabis use disorder was also positively genetically correlated with alcohol use,36 nicotine dependence,48 psychiatric disorders (eg, ADHD,20 schizophrenia,37 major depression),49 and body-mass index (BMI).50
