individual states legalized marijuana; few have focused on the policy effects of the Ogden Memo (56). Three studies that have compared pre- and post-2009 trends (in an effort to capture potential effects of the federal shift in policy) have all found measurable differences in risk perception (51), an increased number of drivers involved in motor vehicle fatalities who had positive toxicology tests for cannabis (55), and an increase in unintentional pediatric ingestions of marijuana products (57). Further research is needed to clarify the relationships among decriminalization, legalization, and prevalence.
