Policy changes can exert powerful effects on expression or suppression of genetic vulnerability. For instance, Boardman and colleagues found that genetic factors played a significantly greater role in smoking cessation in those who quit after bans and restrictions on smoking had begun to be imposed. These analyses suggested that even crude indices of policy change can impact the contribution of genetic influences. In the next sections, we shift our focus from the etiology of co-occurring cannabis and tobacco involvement to a discussion of its possible consequences.
