In recent years there has been a growing accumulation of studies examining the heritability of cannabis-related phenotypes. Verweij et al. (2010) identified 28 studies reporting the heritability of cannabis use initiation and 27 studies reporting the heritability of problematic cannabis use (typically abuse or dependence symptomatology). Summing results from these studies using meta-analytic techniques, they reported that for initiation of cannabis use, 48% of variance in liability in males and 40% of the variance in females could be attributed to additive genetic factors while the estimates for problematic cannabis use were 51% and 59%, respectively. Modest genetic influences on availability of cannabis have also been reported (Gillespie et al., 2007).
