Since 2002, perceived availability of marijuana among young people has fallen dramatically nationwide.
"Between 2002 and 2015, we observed a 27% overall reduction in the relative proportion of adolescents ages 12-17-and a 42 percent reduction among those ages 12-14-reporting that it would be "very easy" to obtain marijuana. This pattern was uniformly observed among youth in all sociodemographic subgroups. ... Despite the legalization of recreational and medical marijuana in some states, our findings suggest that ... perceptions that marijuana would be very easy to obtain are on the decline among American youth." (Trends in perceived access to marijuana among adolescents in the United States: 2002-2015, Journal of Studies of Alcohol and Drugs, 2017)
"From 2002 to 2014, ... the perceived availability decreased by 13 percent among persons aged 12-17 years and by three percent among persons aged 18-25 years." (United States Centers for Disease Control, National Estimates of Marijuana Use and Related Indicators - National Survey on Drug Use and Health, United States, 2002-2014, 2016)
Rates of problematic cannabis use by young people has declined 24 percent between 2002 and 2013.
The enactment of medical cannabis laws is not associated with any causal upticks in youth marijuana use
"Of 17 large surveys using difference-in-difference methods spanning different states, periods, and specifications, 16 indicated no MML (medical marijuana laws) effects on adolescent use. Despite differences in methodology, the findings were very consistent: post-MML adolescent cannabis use did not increase compared to pre-MML levels and to national trends in non-MML states during the corresponding years." (U.S. epidemiology of cannabis use and associated problems, Neuropsychopharmacology, 2017)
"The prevalence of past-year cannabis use among youth decreased from 15.8 percent in 2002 to 13.1 percent in 2014. ... Among youth cannabis users, the prevalence of past-year CUD (cannabis use disorder) decreased from 27.0 percent in 2002 to 20.4 percent in 2014." (Cannabis use and cannabis use disorders among youth in the United States, 2002-2014, Journal of Clinical Psychiatry, 2017)
"Using data through 2011, this study found little evidence for an increase in past-30-
day marijuana use, or past-30-day heavy marijuana use, among adolescents in response to state-enacted medical marijuana laws, regardless of most provisions, consistent with findings from other recent studies." (The design of medical marijuana laws and adolescent use and heavy use of marijuana: Analysis of 45 states from 1991 to 2011, Drug and Alcohol Dependence, 2017)
"[T]he results of this study showed no evidence for an increase in adolescent marijuana use after the passage of state laws permitting use of marijuana for medical purposes. ... [C]oncerns that increased marijuana use is an unintended effect of state marijuana laws seem unfounded." (Medical marijuana laws and adolescent marijuana use in the USA from 1991 to 2014: results from annual, repeated cross-sectional surveys, Lancet Psychiatry, 2015)
"There were no statistically significant differences in marijuana use before and after policy change for any state pairing. In the regression analysis, we did not find an overall increased probability of marijuana use related to the policy change. ... This study did not find increases in adolescent marijuana use related to legalization of medical marijuana." (The Impact of State Medical Marijuana Legislation on Adolescent Marijuana Use, Journal of Adolescent Health, 2014)
The passage of adult use cannabis laws is not associated with any causal upticks in youth marijuana use in those jurisdictions that have enacted them
"[A]cross grades 6, 8, 10, and 12, cannabis use indicators have been stable or fallen slightly since I-502's enactment. ... We found no evidence that the amount of legal cannabis sales affected youth substance use or attitudes about cannabis or drug-related criminal convictions." (Washington State Institute for Public policy, I-502 Evaluation and Cost-Benefit Analysis, 2017)
"For adults and adolescents [in Colorado], past-month marijuana use has not changed since legalization either in terms of the number of people using or the frequency of use among users. Based on the most comprehensive data available, past month marijuana use among Colorado adolescents is nearly identical to the national average." (Colorado Department of Public Health and Environment, Monitoring Health Concerns Related to Marijuana in Colorado, 2017)
[M]arijuana use, both among adults and among youth [in Colorado], does not appear to be increasing to date. No change was observed in past 30-day marijuana use among adults between 2014 (13.6 percent) and 2015 (13.4 percent). Similarly, there was no statistically significant change in 30-day or lifetime marijuana use among high school students between 2013 (lifetime: 36.9 percent, 30-day: 19.7 percent) and 2015 (lifetime: 38.0 percent, 30-day: 21.2 percent)." (Lessons learned after three years of legalized, recreational marijuana: The Colorado experience, Preventive Medicine, 2017)
"We can state with some confidence that, even in states that have enacted marijuana liberalization policies, marijuana use among adolescents is not currently increasing. In fact, there is rather compelling evidence that adolescent marijuana use has steadily declined." (Marijuana use among young people in an era of policy change: what does recent evidence tell us?, The American Journal of Drug and Alcohol Abuse, 2016)