New survey data from Colorado indicate that marijuana legalization so far has not led to an increase in pot smoking by teenagers, as prohibitionists warned it would. In the 2013 Healthy Kids Colorado survey, 37 percent of high school students reported that they had ever tried marijuana, down from 39 percent in 2011. The percentage who reported using marijuana in the previous month (a.k.a. "current" use) also declined, from 22 percent in 2011 to 20 percent in 2013. The state Department of Public Health and Environment, which oversees the survey, says those decreases are not statistically significant. But they are part of a general downward trend in Colorado that has continued despite the legalization of medical marijuana in 2001, the commercialization of medical marijuana in 2009 (when the industry took off after its legal status became more secure), and the legalization of recreational use (along with home cultivation and sharing among adults) at the end of 2012:

The earlier numbers come from the CDC's Youth Risk Behavior Survey, to which Colorado contributes data from its own survey. (You can find the state-specific numbers in the reports listed here.) The CDC survey is conducted every other year, but Colorado has not always participated, which is why data for 1999, 2001, 2003, and 2007 are missing. Still, this does not look like what you would expect to see if relaxing restrictions on marijuana led to more underage consumption. In fact, the downward trend during this period is clearer in Colorado than in the country as a whole:

Nationwide, past-month marijuana use by high school students rose between 1995 and 1999, then declined steadily until 2007, when it began a gradual rise that continued through 2013. In Colorado, by contrast, that number rose between 2005 and 2009 but has declined since then. Again, not what you would expect if making marijuana legally available to adults boosted consumption by minors. More detailed and sophisticated analyses, including data from various states with medical marijuana laws, likewise have found no evidence of such an effect.

"Once again, claims that regulating marijuana would leave Colorado in ruins have proven to be unfounded," says Mason Tvert of the Marijuana Policy Project, who was a leader of Colorado's legalization campaign. "How many times do marijuana prohibition supporters need to be proven wrong before they stop declaring our marijuana laws are increasing teen use? They were wrong when they said regulating medical marijuana would do it, and they were wrong when they doubled down and said making marijuana legal for adults would do it."

It is still possible, of course, that legal recreational sales, which began in Colorado only this year, will increase teenagers' access to marijuana (not through direct sales but through diversion from adult buyers), which might lead to an increase in consumption. Colorado officials express a somewhat different concern. According to a press release from the health department, "Health experts worry that the normalization of marijuana use in Colorado could lead more young people to try it." In other words, they worry that allowing adults to legally purchase marijuana for recreational use will encourage teenagers to take a more positive view of cannabis, which will make them more likely to use it. Call it the "permitted fruit" effect. Prohibitionists such as former drug czar Gil Kerlikowske raised the same complaint against medical marijuana laws, but their fears seem to have been misplaced. For what it's worth, the health department reports that "the percentage of students who perceived a moderate or great risk from marijuana use declined from 58 percent in 2011 to 54 percent in 2013," even as marijuana use fell.