Legalization of medical marijuana has both fewer risks and fewer benefits than previously reported, new research shows.

A meta-analysis of 11 studies conducted between 1991 and 2014 shows there is no evidence to support the hypothesis that US medical marijuana laws (MMLs) have led to an increase in the prevalence of marijuana use among adolescents.

“For several years, people have been very concerned about the potential for medical marijuana laws to lead to increases in teen use of marijuana, because early heavy use is associated with impaired neurodevelopment, educational, and occupational achievement,” senior author Deborah Hasin, PhD, professor of epidemiology in psychiatry, Columbia University, New York City, told Medscape Medical News.

“The results were quite clear — MML did not lead to increases in teen marijuana use,” she said.

In an accompanying editorial, investigators concluded that it is “premature” to believe that increased access to medical marijuana may help solve the US opioid crisis.

“The purpose of our editorial was to point out how weak such correlational evidence is in supporting the claim that medical cannabis has reduced opioid overdose deaths,” lead author Wayne Hall, PhD, professor, Center for Youth Substance Abuse Research, University of Queensland, Australia, told Medscape Medical News.

He cautioned US state legislative bodies against “drawing the policy conclusion that they could reduce opioid overdose deaths by either allowing medical use of cannabis or by expanding access to medical cannabis.”

The study was published online February 22 in Addiction.

Unanswered Questions

As of November 2016, 28 states had enacted policies legalizing marijuana use for medical purposes, but “public debate has focused on the potential for MMLs to increase recreational use of marijuana in adolescents,” Hasin and coauthors write.

Hasin’s group previously conducted a study of the effects of MMLs in more than 1 million US teens, who

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