The researchers concluded that youth cannabis use has not increased after states promoted legalisation for medical or adult use in a study published in a leading scientific journal. Instead, the policy change has an overall impact on teen cannabis use that is "statistically indistinguishable from zero," they report.
In fact, it appears that the establishment of certain regulated models of cannabis leads to lower use of the plant among teenagers under certain measures – a finding that directly conflicts with anti-legalisation arguments commonly made by prohibitionists.
The analysis, published by the Journal of the American Medical Association, analysed federal data from the 1993-2019 Youth Risk Behavior Survey in 10 US states, comparing both medical and adult use.
The researchers determined that the adoption of recreational cannabis legalisation was not associated with current marijuana use or frequent marijuana use.
Furthermore, "the adoption of the medical cannabis law was associated with a 6% reduction in the chances of current use of the plant and a 7% reduction in the chances of frequent use."
The study, which received partial funding through a federal grant from the National Institutes of Health, also found that youth cannabis use declined in states where recreational legalisation had been in place for two years or more.
"As more post-legalisation data become available, researchers will be able to draw stronger conclusions about the relationship between regulation and adolescent cannabis use."
The study authors did not attempt to explain why youth may not be using marijuana more often in states that have legalised it, but it is a trend that is not surprising to advocates who have long reasoned that allowing the sale in a regulated environment would harm the illicit market and minimise youth access.
"This study provides additional evidence that legalising and regulating cannabis does not result in increased rates of use among teenagers," Matthew Schweich, deputy director of the Marijuana Policy Project, told Marijuana Moment.
In fact, this suggests that cannabis legalisation laws may be decreasing teen use.
"This makes sense because legal companies are required to strictly verify the identities of their customers," he said. "The unregulated market, which prohibitionists are effectively trying to support, lacks these protections."
The director of the National Institute on Drug Abuse (NIDA), Nora Volkow, also admitted in a recent interview that legalisation had not increased youth use, despite her earlier fears.
On the podcast by Drug Policy Alliance founder Ethan Nadelmann, Volkow said that she "expected marijuana use among teenagers to increase" when states moved to legalise cannabis but admitted that "overall, it hasn't increased." She admitted that reform advocates like Nadelmann were "right" about the impact of policy change on youth.
In May, a federal report also challenged the prohibitionist narrative that legalising cannabis at the state level leads to increased use among young people.
The US Department of Education's National Center for Education Statistics also analysed youth surveys of high school students from 2009 to 2019 and concluded that there was "no measurable difference" in the percentage of 9th-12th graders who reported consuming cannabis at least once in the last 30 days.
In a separate earlier analysis, the Centers for Disease Control and Prevention found that cannabis use among high school students declined during the peak years of the state's legalisation of legal recreational cannabis.
The survey found that there was "no change" in the current rate of cannabis use among high school students from 2009-2019. When analysed using a quadratic shift model, however, lifetime drug use declined during this period.
A federally funded Future Monitoring report released last year found that cannabis use among teenagers "has not changed significantly in any of the three classes for lifetime use, use in the past 12 months, use in the past 30 days, and daily use from 2019-2020."
Another study released by Colorado officials last year showed that cannabis use by youth in the state "doesn't change.
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