may be environmental – one twin study noted that the extent to which the same genetic factors influenced subjective reactions to tobacco and cannabis was modest (74). In addition, implicit cognitive processes (i.e. an expectancy that cannabis smoking is less unpleasant, based on prior experiences with tobacco smoking) may also play a role in cross-drug adaptation. This latter hypothesis implies that, in addition to a predisposition to substance use, some individuals may have a preference for (or an absence of aversion from) smoked substances.
