Year-over-year teen marijuana use fell in most states during that time period, including in Washington, the other state to open recreational marijuana markets in 2014. But that drop wasn't statistically significant.
Conversely, adult marijuana use rose significantly in Colorado over the same time period. Among Coloradans ages 26 and older, past-year marijuana use rose from 16.80 percent in 2013/2014 to 19.91 percent in 2014/2015. Annual adult marijuana use was up in most states during the same time frame. The legal marijuana markets in Colorado, Washington and elsewhere feature strict age and purchasing limits.
This federal data released this week is the first clear evidence of a drop in teen marijuana use in Colorado following legalization. Legalization supporters have long argued that the best way to prevent underage marijuana use is to legalize and regulate the drug.
The federal data doesn’t speak to what, exactly, is behind the decrease in teen marijuana use in Colorado. Broadly speaking, adolescent substance use has declined across the board in recent years.
The federal survey data do show that the overall rate of teen marijuana use remains higher in Colorado than it is in any other state. But that trend began well before legalization, as the chart below of monthly marijuana use in Colorado and the United States shows.
In either case, the overall trend — flat or falling teen use — appears to support legalization supporters’ arguments that liberalizing marijuana policies will not pose a serious public health threat to adolescents.