We also found that the link between cannabis involvement and SI was strongly influenced by shared genetic influences. This is consistent with pre-clinical evidence regarding the role of the endocannabinoid system in both the behavioral effects of cannabis and the regulation of depressive and anhedonic mood states (Gorzalka and Hill, 2011). One prior study of 277 discordant twins (Lynskey et al., 2004; utilizing data from Sample 1) found that CUD was associated with a 2.5–2.9 increased OR of SI and attempt. In other words, even when individuals were matched for their segregating genes and early family environment, a history of CUD significantly increased the likelihood of STB, suggesting the possibility of causal/individual-specific factors in this association. We found support for such individual-specific factors influencing both cannabis involvement and SI in male and female twins (rE=0.21). Furthermore, due to the smaller sample size, twin models with SANP could not be fit to the data.
