Study shows decline in teen use of marijuana where recreational use is legal

Study shows decline in teen use of marijuana where recreational use is legal
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Marijuana use among teens dropped in states that legalized the substance's recreational use, according to research published Monday.

Laws that legalized recreational marijuana, which have been passed in 10 states and Washington, D.C., were associated with an 8 percent drop in the number of high schoolers who said they used marijuana in the last 30 days, and a 9 percent drop in the number who said they'd used it at least 10 times in the last 30 days, according to the study published in the medical journal JAMA Pediatrics.

Researchers did not find a statistical link between medical marijuana laws and changes in youth usage.

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"Just to be clear, we found no effect on teen use following legalization for medical purposes, but evidence of a possible reduction in use following legalization for recreational purposes," Mark Anderson, an associate professor at Montana State University who worked on the research, told CNN.

"Because our study is based on more policy variation than prior work, we view our estimates as the most credible to date in the literature," he said.

The researchers analyzed data from 1993 to 2017 on about 1.4 million high school students in the United States from the U.S. Centers for Disease Control and Prevention's annual national Youth Risk Behavior Surveys.

They found an association, not a causal relationship.

"Because many recreational marijuana laws have been passed so recently, we do observe limited post-treatment data for some of these states," Anderson added to CNN. "In a few years, it would make sense to update our estimates as more data become available."