Continual monitoring of new cannabis policies is recommended
Although it is still too early to evaluate the impact of new cannabis policies, the evidence collected to date in the United States points to an increase in cannabis use in states where referendums have led to the legalization of recreational marijuana use. New challenges have emerged in some states of the United States (notably Colorado), including the marketing of unregulated cannabis products (edibles) with a high content of tetrahydrocannabinol (THC). Moreover, there is evidence of an increasing number of cannabis users driving under the influence, as well as an increase in cannabis-related emergency room visits and hospitalizations. However, cannabis-related arrests and court cases related to cannabis offences have decreased. All of these outcome measures would need to be rigorously monitored and evaluated over a period of time before a final assessment can be made.
https://www.unodc.org/doc/wdr2016/WORLD_DRUG_REPORT_2016_web.pdf