Teen marijuana use down despite greater availability

The Johns Hopkins Bloomberg School of Public Health researchers say, however, that marijuana use is significantly greater than the use of other illegal drugs, with 40 percent of teens in 2013 saying they had ever smoked marijuana. That number was down from 47 percent in 1999 but up from 37 percent in 2009. By contrast, just three percent had ever tried methamphetamines in 2013 as compared to nine percent in 1999.

The findings, published online this month in the journal Drug and Alcohol Dependence, also suggest that a gender gap in marijuana use -- where boys outnumbered girls as users of the drug -- is shrinking, with males and females now using marijuana at similar rates. And while white and black teens once used marijuana at similar rates, now blacks report using the drug more often.

Marijuana policy has undergone significant changes over the past 20 years. Since 1996, 34 states have passed legislation removing criminal sanctions for medical use of marijuana. Eleven states have passed laws decriminalizing possession of small amounts of marijuana, adding to nine that passed such laws in the late 1970s. Four states have passed laws allowing for the recreational use of marijuana for people over 21.

"People have been very quick to say that marijuana use is going up and up and up in this country, particularly now that marijuana has become more normalized," says study leader Renee M. Johnson, PhD, MPH, an assistant professor in the Department of Mental Health at the Bloomberg School. "What we are seeing is that since 1999 -- three years after medical marijuana was first approved -- the rates of marijuana use have actually fallen. But we will be watching those states where recreational marijuana use has been legalized to see if that leads to increased use among teens."

Johnson says she isn't sure why rates of marijuana use have fallen since 1999. The 1980s and the early 1990s were a time when it was very difficult to obtain marijuana due to a federal crackdown on illicit drugs and strong anti-drug education programs, such as the "just say no" campaign. But use shot back up in the late 1990s. While rates of use have been falling since 1999, they started to rise again in 2009. Time will tell, she says, whether the recent uptick in marijuana use is just a statistical blip or a sign that greater availability of the drug is leading to a reversal of the decade-long downward trend.

Colorado, Oregon, Alaska, Washington and the District of Columbia have laws that legalize some recreational use of marijuana, which have only been passed in recent years. The longer those laws are in place, Johnson says, the more likely there could be an effect on marijuana use among teens -- even though it is technically illegal to use pot under age 21. Johnson and her colleagues are studying the laws in Colorado and Washington state, whose laws went into effect November 2012 and over 2013, respectively.

Johnson and her colleagues examined data from the National Youth Risk Behavior Survey, a biennial school-based survey of students in grades nine through 12, which gathered information from more than 115,000 adolescents throughout the U.S. They analyzed information from 1999 to 2013. The survey has been conducted by the U.S. Centers for Disease Control and Prevention since 1990.

Use of other illegal drugs including hallucinogens and cocaine has also fallen throughout the time period, as has use of alcohol and cigarettes among teens. In 2013, 41.1 percent of the teens surveyed said they had smoked cigarettes in their lifetime, while 40.7 percent said they had used marijuana in their lifetime. The rates of cigarette smoking are down from 70.4 percent in 1999. Those who said they had ever tried alcohol fell from 81 percent in 1999 to 66.2 percent in 2013.

The survey found that in 1999, 51 percent of boys and 43 percent of girls had ever used marijuana, and by 2013, 42 percent of boys and 39 of girls say they had used it in their lifetimes. In 1999, 29 percent of both white and black teens reported having used marijuana; whereas in 2013, 29 percent of black teens and 20 percent of white teens had used the drug.

Even though marijuana use is lower today than it was 15 years ago, Johnson says it may be time to promote programs that educate high school students about the specific harms of marijuana use -- something that mostly hasn't been done. The focus has been more on preventing teens from using tobacco and alcohol.

"We've done a really good job in public health of alcohol and tobacco use prevention," she says. "We haven't done the same with marijuana. We would do well to follow the lessons learned from those programs, which have been pretty successful."