

Vendors and growers prepare their displays for card-carrying medical marijuana patients attending Los Angeles' first-ever cannabis farmer's market July 4. (Frederic J. Brown/AFP/Getty Images)

Opponents of marijuana legalization are rapidly losing the battle for hearts and minds. Simply put, the public understands that however you measure the consequences of marijuana use, the drug is significantly less harmful to users and society than tobacco or alcohol.

But opponents still have one trick up their sleeves, and it's proven to be a powerful and effective one: the notion that relaxed regulations on marijuana will lead to a rise in marijuana use among children and teens. Florida voters, for instance, will decide whether to legalize medical marijuana this November. Organizations opposing the measure have built their campaigns around fears about underage use.



(Image via Don't Let Florida Go To Pot)

The group Don't Let Florida Go To Pot greets visitors to its Web site with the above image, warning that medical marijuana will turn your child into a hoodie-wearing, pot-smoking thug.



(Image via voteno2.org)

Vote No On 2 features another hoodie-clad youngster on its home page, no doubt contemplating the depravity of his existence after medical marijuana. Florida voters don't seem to be buying any of this, though: Medical marijuana currently enjoys nearly 90 percent support in the state.

More to the point, the notion that medical marijuana leads to increased use among teenagers is flat-out wrong. A new study by economists Daniel Rees, Benjamin Hansen and D. Mark Anderson is the latest in a growing body of research showing no connection -- none, zero, zilch -- between the enactment of medical marijuana laws and underage use of the drug.

The authors examined marijuana trends in states that passed medical marijuana laws. They tracked self-reported pot use by high school students in the years leading up to and following the enactment of these laws. They conclude that the effects of medical marijuana on teen use are "small, consistently negative, and never statistically distinguishable from zero."

The chart above shows the trend in teen marijuana use, as measured by state Youth Risky Behavior Surveys, in Alaska, Arizona, Colorado, Delaware, Maine, Mississippi, Montana, Nevada, New Mexico and Vermont. The x-axis is standardized to track the three-year periods before and after each state passed its medical marijuana law. The lines are essentially flat.

I asked study co-author Daniel Rees if there were any significant changes within individual states. He told me that "no single state stood out -- the effect of massing a medical marijuana law on youth consumption appears to be zero across the board." These results are consistent with earlier research showing little change in youth pot consumption in Los Angeles after marijuana dispensaries opened there.

The authors verified their work by running a number of regression tests and examining youth drug use data from other sources, too. They found that, if anything, passage of medical marijuana laws had a slight negative effect on teen use. In a forthcoming paper, Rees and Anderson hypothesize that this might be because "legalization allows suppliers to sell to adults with some assurance of not being prosecuted, while selling marijuana to a minor is still a risky proposition even with the legalization of medical marijuana."

There's little doubt that, like alcohol or tobacco, marijuana use can potentially be harmful to teens, particularly to heavy users. But this paper, like others before it, provides straightforward evidence that there is no link between medical marijuana laws and teen marijuana use. If Florida's concerned citizens are truly worried about teen drug use, according to this paper they'd be better off advocating in favor of legalizing medical marijuana there.