Study finds legalized medical marijuana doesn't lead to increased teen use

UO economist Benjamin HansenEUGENE, Ore. — (June 18, 2012) — While marijuana use by teens has been increasing since 2005, an analysis of data from 1993 through 2009 by economists at three U.S. universities found no evidence that legalized medical marijuana laws have contributed to more use of the drug by high school students.

"There is anecdotal evidence that medical marijuana is finding its way into the hands of teenagers, but there's no statistical evidence that legalization increases the probability of use," said Daniel I. Rees, professor of economics at the University of Colorado Denver. Co-authors of the study were Benjamin Hansen of the University of Oregon and D. Mark Anderson of Montana State University.

The study examined the relationship between the legalization of medical marijuana and marijuana consumption using nationally representative data on high school students from the Youth Risky Behavior Survey (YRBS). During that time, 13 states legalized medical marijuana. Seventeen states and the District of Columbia now have such a law and legislation is pending in seven other states.

Audio from Benjamin Hansen:

Background of the study

The findings

"This result is important given that the federal government has recently intensified its efforts to close medical marijuana dispensaries," said Hansen, who studies risky behaviors. "In fact, the data often showed a negative relationship between legalization and marijuana use.”

Federal officials, including the director of the Office of National Drug Control Policy, and some law enforcement agencies argue that the legalization of medical marijuana has contributed to the recent increase in marijuana use among teens in the United States and have targeted dispensaries operating within 1,000 feet of schools, parks and playgrounds.

According to the 2011 report "Monitoring the Future National Results on Adolescent Drug Use," prepared annually by the University of Michigan Institute for Social Research, marijuana use by 10th and 12th graders has risen in the last three years, with roughly one in 15 high school seniors smoking marijuana daily or near-daily. The report, cited in the economists' study, surveyed 46,700 students in the eighth, 10th and 12th grades, in 400 secondary schools.

The new study "Medical Marijuana Laws and Teen Marijuana Use" currently is a non-peer-reviewed working paper made available by the Institute for the Study of Labor (IZA), a private, non-profit independent research institute based in Bonn, Germany, that conducts internationally oriented labor market research.

Researchers examined the relationship between legalization and various outcomes such as marijuana use at school, whether the respondent was offered drugs on school property, alcohol use and cocaine use. They found no evidence that legalization led to increases in marijuana use at school, the likelihood of being offered drugs on school property or the use of other substances.

In addition to national YRBS data, the researchers drew on state YRBS data for 1993-2009 and data from the National Longitudinal Survey of Youth 1997. The two data sets contain information on self-reported marijuana use. They also examined the Treatment Episode Data Set, which contains information on whether patients at federally funded drug treatment facilities tested positive for marijuana upon admission. The results of this analysis suggested that the legalization of medical marijuana was unrelated to the likelihood that patients ages 15-20 tested positive for marijuana.

"We are confident that marijuana use by teenagers does not increase when a state legalizes medical marijuana," said Montana State's Anderson, professor of economics who studies health economics, risky behavior and crime.

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The University of Oregon is among the 108 institutions chosen from 4,633 U.S. universities for top-tier designation of "Very High Research Activity" in the 2010 Carnegie Classification of Institutions of Higher Education. The UO also is one of two Pacific Northwest members of the Association of American Universities.

Media Contacts: Jim Barlow, director of science and research communications, 541-346-3481, and David Kelly, Media Relations, UC Denver, 303-503-7990,

Sources: Benjamin Hansen, assistant professor of economics, University of Oregon, 541-346-4658, ; Daniel I. Rees, professor of economics, UC Denver, 303-315-2037, ; D. Mark Anderson, assistant professor of agricultural economics and economics, Montana State University, 406-366-0921,

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