Parental drug problems were significantly associated with a more rapid transition to both opportunity and dependence, in line with existing research relating to opportunity (Benjet et al., 2013). This factor most clearly demonstrated changes in the magnitude of effect size between transitions, and given the especially strong association with opportunity to use cannabis it is plausible that parental drug problems facilitate an environment in which drug access is increased, whether this is indirectly or directly through parents. Alternatively, cannabis availability has previously been shown to be influenced by genetic effects (Gillespie et al., 2009), and the present finding may represent a genetic liability to creating drug use opportunities.
