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James Poelzer, CEO of Agrima Botanicals, handles seedling marijuana plants at his medical marijuana production facility in Maple Ridge, B.C., on January 10, 2014. (Rafal Gerszak for The Globe and Mail)
James Poelzer, CEO of Agrima Botanicals, handles seedling marijuana plants at his medical marijuana production facility in Maple Ridge, B.C., on January 10, 2014. (Rafal Gerszak for The Globe and Mail)

Legalizing medical marijuana doesn’t boost teen use Add to ...

A rise in marijuana use among American teenagers over the past 20 years has no significant tie to the legalization of marijuana for medical use in many states, according to a research paper.

Comparing surveys of marijuana use by adolescents conducted annually by the federal Centers for Disease Control and Prevention, researchers found the probability that a high-school student had used pot in the previous 30 days was no more than 0.8 per cent higher in legal states compared with states that had not approved medical marijuana.

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“Our results are not consistent with the hypothesis that the legalization of medical marijuana caused an increase in the use of marijuana among high school students,” wrote D. Mark Anderson of Montana State University, Daniel Rees of the University of Colorado, and Benjamin Hansen of the University of Oregon.

Twenty-one states and the District of Columbia have legalized the use of marijuana for medical purposes, while two states, Colorado and Washington, now allow personal recreational use by adults over the age of 21.

Alaska and Oregon are set to vote on legalization for recreational use in November, while supporters of full legalization in the country’s capital say they have enough signatures to put the measure on the ballot.

Marijuana remains illegal under U.S. federal law.

Some opponents of legalization are concerned that it will increase use among teens. According to Monitoring the Future, an organization financed by the National Institute on Drug Abuse that has surveyed drug use among teens since 1975, 36 per cent of high-school seniors surveyed in 2013 said they used pot in the previous year, while 6.5 per cent said they used it almost every day.

Use among Grade 12 students peaked in 1979 at 51 per cent and fell to a low of 22 per cent in 1992. Use slowly increased after 1992, but it has levelled since 2011.

A study published in the Annals of Epidemiology in 2011 found use among adolescents in medical marijuana states had risen, but concluded that more research was needed to draw a causal conclusion.

Further, it found that between 2002 and 2008, use among teens was highest in states where the drug was legal, but it was also already high in those states prior to legalization.

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