Seventeen states and the District of Columbia have legalized medical marijuana since 1996, when California became the first. A recent study by researchers at the Columbia’s Mailman School of Public Health in New York suggested that teens are more likely to use marijuana and have a lower perception of its risk in those states that allow it for medical use compared with teens in states that don't allow medical use, though the cause for the difference was unclear. A national drug survey looked at average usage rates in 2008 and 2009 among 12- to 17-year-olds.
WHERE MEDICAL MARIJUANA IS LEGAL
MARIJUANA USE IN PAST YEAR AMONG YOUTHS AGES 12 TO 17
TEEN ATTITUDES TOWARD USE OVER TIME
Public health officials and brain researchers say they worry that legalization of marijuana for medical use is causing teens to see it as less harmful, even as some recent research has found that marijuana dependency among teens may harm brain development and mental health over the long term. Twelfth-graders interviewed in 2011 were about as likely as those interviewed in 1975 to say they saw "great risk" in smoking marijuana regularly, a long-running national survey found.