Opponents of marijuana law reform, including those who lobby against the plant’s therapeutic use when authorized by a physician, allege that the adoption of such laws will result in a significant increase in pot use by young people.  
 
For example, in a recent open letter to US Attorney General Eric Holder and DEA Administrator Michele Leonhart, David Evans, executive director of the Drug Free Schools Coalition wrote: “The damage of marijuana -- and these laws -- is clear. Legalization of marijuana for ‘medical’ use and recreational use in those states has resulted in more marijuana use, particularly among young people.”

Former Drug Czar Gil Kerlikowske made similar claims during his tenure as the nation’s top anti-drug cop, stating: “These last couple years, the amount of attention that’s been given to medical marijuana has been huge. And when I've done focus groups with high school students in states where medical marijuana is legal, they say ‘Well, if it’s called medicine and it’s given to patients by caregivers, then that’s really the wrong message for us as high school students.’”

But a new study shows, not surprisingly, that these prohibitionists’ claims are altogether false. 

In a just published working paper by the National Bureau of Economic Research, a non-partisan research organization based in Cambridge, Massachusetts, investigators from the University of Colorado at Denver, the University of Oregon, and Montana State University assessed federal data on youth marijuana use and treatment episodes for the years 1993 to 2011 -- a time period when 16 states authorized medical cannabis use. They reported: “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.  In fact, estimates from our preferred specification are small, consistently negative, and are never statistically distinguishable from zero.”

Or, as Washington Post contributor Chris Ingraham put it, “the notion that medical marijuana leads to increased use among teenagers is flat-out wrong. ...[R]esearch show[s] no connection -- none, zero, zilch -- between the enactment of medical marijuana laws and underage use of the drug.”

He’s right. A separate analysis published in April in the Journal of Adolescent Healthsimilarly determined, “This study did not find increases in adolescent marijuana use related to legalization of medical marijuana ... This suggests that concerns about ‘sending the wrong message' may have been overblown.”

Moreover, a 2013 study published in the American Journal of Public Health also concluded that the  passage of statewide medical marijuana has had no "statistically significant ...  effect on the prevalence of either lifetime or 30-day marijuana use" by  adolescents residing in those states. 

Likewise, a 2012 study  by researchers at  McGill University in Montreal reported: "[Passing MMLs (medical marijuana  laws) decreased past-month use among adolescents ... and had no discernible  effect on the perceived riskiness of monthly use. ... [These] estimates suggest  that reported adolescent marijuana use may actually decrease following the  passing of medical marijuana laws."