In cotwin-control comparisons, the 293 respondents who used cannabis early were at significantly greater risk of trying other illegal drugs (see Table 2). In unadjusted models, early-users were 1.89-3.63 times more likely to have tried other substances. Furthermore, this risk was not attenuated when the models were adjusted for the covariates (OR: 2.71-4.09). Early cannabis use was also a significant predictor of any illegal drug abuse/dependence (but not cannabis abuse/dependence, or abuse/dependence for illegal substances other than cannabis). In models adjusted for covariates, early cannabis users were about 2.0 times more likely to have an illegal drug abuse/dependence diagnosis. Early cannabis users were also about 2.4 times more likely to be alcohol dependent than were their discordant cotwins (see Table 2).
