For years drug czar Gil Kerlikowske has argued that laws allowing medical use of marijuana and efforts to legalize recreational use encourage teenagers to smoke pot. According to Kerlikowske, it is irresponsible even to advocate less punitive, more tolerant marijuana laws because such talk sends "the wrong message" to the youth of America. That tale has never fit the facts very well, whether you look at cannabis consumption trends in relation to the enactment of medical marijuana laws or compare states with such laws to states without them. The latest data from the government-sponsored Monitoring the Future Study cast further doubt on Kerlikowske's theory, indicating that marijuana use has declined among eighth-graders and 10th-graders while remaining steady among 12th-graders even as pot tolerance has hit record highs. Conversely, pot smoking by high school students remains substantially below the levels recorded in the late 1970s, when the idea of legalizing marijuana was much less popular.

In the 2012 survey, 6.5 percent of eighth-graders admitted smoking pot during the previous month, compared to 7.2 percent last year and 8 percent in 2010. Past-month use by 10th-graders fell from 17.6 percent to 17 percent (still a bit higher than the 16.7 percent recorded in 2010). Among seniors, this number rose slightly, from 22.6 percent to 22.9 percent, a difference that was not statistically significant. "After four straight years of increasing use among teens," say the University of Michigan researchers who conduct the survey, "annual marijuana use showed no further increase in any of the three grades surveyed in 2012." Maybe the upward trend will resume next year, after the kids digest the wrong message sent by the legalization of marijuana (for adults 21 and older) in Colorado and Washington.

More bad news for drug warriors and their panic-promoting pals in the press: The share of high school seniors who admitted consuming synthetic marijuana in the previous year remained steady (at 11.3 percent); the percentage of students reporting any use of the synthetic stimulants known as "bath salts" was "very low"; and use of Salvia divinorum fell in all three grades covered by the survey.