SACRAMENTO — Bucking dire predictions by anti-drug warriors, the 10 states that approved medical marijuana laws over the last decade have experienced sharp declines in cannabis use among teenagers, according to a new study by a marijuana advocacy group.
California has seen usage among ninth-graders drop 47% since 1996, the year the state became the nation's first to legalize medical marijuana. Over the same period, the nation as a whole experienced a 43% decline among eighth-graders.
The study, released today, is based on data from national and state surveys, which show a drop in marijuana use by teens.
Although debate over medical marijuana is often shaded by concerns about increasing drug abuse among young people, the report suggested the opposite has been true.
The study's authors were Mitch Earleywine, a State University of New York psychology professor, and Karen O'Keefe, a legislative analyst with Marijuana Policy Project, the organization that commissioned the research based on state and federal data.
That data "strongly suggests" that approval of medical marijuana has not increased recreational use of cannabis among adolescents, Earleywine and O'Keefe concluded. And the decline in many of the states with medical marijuana laws is "slightly more favorable" than trends nationwide, they said.
California, Washington and Colorado have all experienced greater drops in marijuana usage than have occurred nationwide. Only three states with medical marijuana laws -- Maine, Oregon and Nevada -- have lagged behind the national drop in teen marijuana use, the report said.
"If medical marijuana laws send the wrong message to children," the authors said, widespread attention to the debate "would be expected to produce a nationwide increase in marijuana use, the largest increase in those states enacting medical marijuana laws. But just the opposite has occurred."
Tom Riley, of the president's Office of National Drug Control Policy, said the drop in teen drug use across the nation is attributable to the federal anti-drug advertising campaign in recent years, including $125 million spent during the federal fiscal year that ends Oct. 1.
Medical marijuana has only clouded that pitch, he said.
"It's foolish to give kids a message that marijuana can be helpful to them," Riley said, adding that all Americans "should be glad that teen drug use is going down. If the drug legalizers are recognizing that, too, I think that says something."
But the researchers sketched a different hypothesis: that medical marijuana shifted the perception among some teens about pot.
"Perhaps medical marijuana laws send a very different message," they wrote. Teens may increasingly consider pot "a treatment for serious illness, not a toy, and requires cautious and careful handling."
The most extensive available data was in California, where a survey of about 6,000 students every two years showed that pot use among teens was climbing before passage of the 1996 medical marijuana law. For all grades, marijuana use dropped significantly between early 1996 and 2004, with the biggest downward shift among ninth-graders.
Between 1996 and 2004, the number of high school freshmen in the state who reported using pot in the last 30 days dropped 47%, while the number of freshmen who had tried cannabis at least once dropped 35%.