Washington State Data On Marijuana Use Following Enactment of I-502
"In these initial investigations, we found no evidence that I-502 enactment, on the whole, affected cannabis abuse treatment admissions. Further, within Washington State, we found no evidence that the amount of legal cannabis sales affected cannabis abuse treatment admissions.
"The bulk of outcome analyses in this report used the within-state approach to focus on identifying effects of the amount of legal cannabis sales. We found no evidence that the amount of legal cannabis sales affected youth substance use or attitudes about cannabis or drug-related criminal convictions.
"We did find evidence that higher levels of retail cannabis sales affected adult cannabis use in certain subgroups of the population. BRFSS respondents 21 and older who lived in counties with higher levels of retail cannabis sales were more likely to report using cannabis in the past 30 days and heavy use of cannabis in the past 30 days.
"We also found two effects that are difficult to interpret. Among the portion of the population aged 18 to 21, BRFSS respondents living in counties with higher sales were less likely to report using cannabis in the past 30 days, in some analyses. It may be that legal cannabis sales have made cannabis more difficult to access by persons below the legal age, for instance, by reducing black market supply through competition.
"We also found that in the portion of the BRFSS sample who smoked cigarettes, respondents living in counties with higher levels of legal cannabis sales were less likely to report past-month cannabis use. It is particularly difficult to explain why increased sales would lead to lower cannabis use among cigarette smokers."
Darnell, A.J. & Bitney, K. (2017). I-502 evaluation and benefit-cost analysis: Second required report. (Document Number 17-09-3201). Olympia: Washington State Institute for Public Policy, September 2017, p. 34.