Data from the Youth Risk Behavior Surveys between 1993 to 2017 covering 27 states and Washington, D.C., before and after "medical" marijuana laws were adopted and 7 states from before and after recreational marijuana laws were adopted covering more than 1.4 million high school students finds that marijuana laws appear to be associated with a decrease in the odds of marijuana use in the past 30 days or frequent marijuana use after medical marijuana laws were passed.

The reasons may be that once it became legal marijuana was no longer cool, it may be because teens recognize that marijuana is not healthier to inhale than cigarettes (a fact lost on policymakers) and it may be that it actually got more difficult for youths to obtain marijuana once it required identification and not just a creep who hangs out selling drugs to children.

Whatever the reason, this is good news.

Now that 33 states and the District of Columbia have passed medical marijuana laws, and 10 states plus the District of Columbia for recreational use, public health nonprofits like ours have been concerned that legalization for bogus medicinal, or recreational, purposes will encourage marijuana use among youth. Repeated marijuana use during adolescence is linked to long-lasting changes in brain function that adversely affect educational, professional, and social outcomes, just like any other drug.

Data have been in conflict, the problem with accepting surveys as evidence. Monitoring the
Future found increased marijuana use among 8th and 10th graders after it was legalized for recreational use in Washington State but no association between legalization and adolescent marijuana use in Colorado. This survey data was 1,414,826 with estimated odds ratios of marijuana use and frequent marijuana use. The authors found that recreational marijuana laws were associated with an 8% decrease in the odds of marijuana use and a 9% in the odds of frequent marijuana use.