Recreational marijuana laws were associated with a decrease in the odds of both teens trying marijuana and frequently using it. (Getty Images)

Researchers say the decrease may be from dispensaries making it more difficult to obtain marijuana.

Marijuana use among teens has not increased in states that have passed medical or recreational marijuana laws in the past 25 years, a new study finds – in fact, legalization may be making it more difficult for teens to obtain pot.

Using data from national and state Youth Risk Behavior Surveys from 1993 to 2017, researchers from Montana State University, University of Oregon, University of Colorado–Denver and San Diego State University examined states that had legalized marijuana for recreational or medical use and the likelihood of marijuana use in the past 30 days among high school students. The study used data from 27 states and the District of Columbia, where medical marijuana has been legalized, and seven states where recreational marijuana has been legalized during the 25-year time period.

Recreational marijuana laws were associated with a 8% decrease in the likelihood of teens trying marijuana as well as a 9% reduction in the odds of frequent marijuana use, the study found. Meanwhile, medical marijuana laws had no noticeable effect on marijuana use among teens.

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"There was no evidence that the legalization of medical marijuana encourages marijuana use among youth," and "marijuana use among youth may actually decline after legalization for recreational purposes," the study, published in JAMA Pediatrics on Monday, said.

The study authors said the estimated decrease may be because "it is more difficult for teenagers to obtain marijuana as drug dealers are replaced by licensed dispensaries that require proof of age."

The study, which received funding support from the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health, echoes previous research that found rates of overall marijuana use by 12th-graders have remained fairly steady despite more states legalizing marijuana for medical or recreational use in recent years.

More than 1 in 5 high school seniors nationwide reported use of an illicit drug in the past month in 2018, with marijuana the leading choice, according to the 2018 Monitoring the Future survey, funded by the National Institute on Drug Abuse.

