In its latest report on marijuana legalization in Colorado, the Rocky Mountain High Intensity Drug Trafficking Area (RMHIDTA), a federally sponsored anti-drug task force, continues to claim that cannabis consumption by teenagers is on the rise in that state. The most recent data from the survey RMHIDTA likes to cite indicate that is not true.

"Youth past month marijuana use increased 12 percent in the three-year average (2013-2015) since Colorado legalized recreational marijuana compared to the three-year average prior to legalization (2010-2012)," RMHIDTA says. But according to newly published Colorado numbers from the National Survey on Drug Use and Health (NSDUH), the prevalence of past-month marijuana use among 12-to-17-year-olds fell significantly in 2015-16 and is now lower than it was prior to legalization.

That rate rose from about 10.5 percent in 2011-12, before legalization, to 11.2 percent in 2012-13, which includes the first year of legal possession and home cultivation, and 12.6 percent in 2013-14, which includes the first year of legal recreational sales. (The numbers are reported in two-year sets because the state-level samples are relatively small.) The post-legalization increases were not statistically significant, and the rate now has fallen for two years in a row, to 11.1 percent in 2014-15 and 9.1 percent in 2015-16. That last drop was statistically significant.

The numbers for Washington state, where voters also approved a legalization initiative in November 2012, show a similar pattern, rising from 9.5 percent in 2011-12 to 10.1 percent 2013-14 before falling to 9.2 percent in 2014-15 and 7.9 percent in 2015-16. Unlike in Colorado, neither of those drops was statistically significant.

As I've said before, it is plausible that legalizing marijuana for adults would boost adolescent consumption by increasing availability through diversion from buyers 21 or older, if not by changing teenagers' attitudes toward cannabis. But there is still little evidence that is happening, notwithstanding the assertions of prohibitionists like the folks at RMHIDTA.