Adolescents who saw advertising for medical marijuana were more likely to either report using marijuana or say they planned to use the substance in the future, according to a new RAND Corporation study.

Studying more than 8,000 Southern California middle school students, researchers found that youth who reported seeing any ads for medical marijuana were twice as likely as peers who reported never seeing an ad to have used marijuana or report higher intentions to use the drug in the future. The study was published online by the journal Psychology of Addictive Behaviors.

Researchers say the study — the first to explore a link between marijuana advertising and youth behavior — still cannot directly address whether seeing ads cause marijuana use. However, the study does raise questions about whether there is a need to revise prevention programming for youth as the availability, visibility and legalization surrounding marijuana changes.

“As prohibitions on marijuana ease and sales of marijuana become more visible, it's important to think about how we need to change the way we talk to young people about the risks posed by the drug,” said Elizabeth D'Amico, lead author of the study and a senior behavioral scientist at RAND, a nonprofit research organization. “The lessons we have learned from alcohol — a substance that is legal, but not necessarily safe — may provide guidance about approaches we need to take toward marijuana.”

Over the past several years, medical marijuana has received increased attention in the media and use of the drug has increased across the United States, with the number of frequent marijuana users increasing by 40 percent since 2006.

Advertising for medical marijuana services has appeared on billboards, in newspapers and even on television. Many medical marijuana dispensaries have visible storefronts, as well.

RAND researchers analyzed information collected from 8,214 students enrolled in 6th, 7th and 8th grade who attended 16 Southern California middle schools during 2010 and 2011. The students were asked each year about exposure to medical marijuana advertising, marijuana use and their intentions about whether to use marijuana in the future.

During the first survey, 22 percent of the students reported seeing at least one advertisement for medical marijuana over the past three months and the rate jumped to 30 percent the following year.

Seeing advertisements for medical marijuana was related to middle school adolescents' intentions to use marijuana and their actual marijuana use one year later. Researchers say this is particularly important given that the mean age of adolescents surveyed was 13 and initiation of marijuana use during early adolescence is associated with poor school performance, neuropsychological performance deficits and further use of other illicit drugs, such as heroin and cocaine.

Researchers say they could not determine whether adolescents who were predisposed to use marijuana paid more attention to marijuana advertising or whether the advertising may have influenced adolescents' attitudes toward the drug.

“Given that advertising typically tells only one side of the story, prevention efforts must begin to better educate youth about how medical marijuana is used, while also emphasizing the negative effects that marijuana can have on the brain and performance,” D'Amico said.

The findings also emphasize the need for a policy discussion about whether regulations may be needed to limit advertising about marijuana for both medical and recreational use, such as the regulations in place that govern advertising of alcohol and tobacco.

Support for the study was provided by the National Institute of Alcohol Abuse and Alcoholism.

Other authors of the study are Jeremy N.V. Miles and Joan S. Tucker.

The medical marijuana advertising study is from ongoing prevention and intervention efforts conducted by RAND researchers, who have developed several group-based interventions for adolescents. Information about the programs is available at groupmiforteens.org.

RAND Health is the nation's largest independent health policy research program, with a broad research portfolio that focuses on health care costs, quality and public health preparedness, among other topics.

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