1. "Openness" is the personality trait of the 5 factor model most closely associated with drug use. Openness also most closely correlates to intelligence amount the 5 factors. Those are coincidental factors not suggesting more intelligent people favor drug use disproportionately.
2. Risk taking behavior, or more precisely actions benefiting from exceptionally low neuroticism, is not a personality facet. Its a result of faster than normal gamma-globulin uptake in the amygdala. Such people do not associate a fear response to stimulus associated decision criteria and as such prioritize things differently. These people tend to have a very low incidence of drug use because they are less capable of feeling thrills and fears.