In the fight against marijuana reform, opponents of legalization have repeatedly trotted out a scare line designed to prod voters into backing away from real change. Legalizing the drug, they say, will lead more teens to use it.

teen marijuana useBut a new study calls that line of reasoning into serious doubt. Scientists in New York and Michigan pooled a massive amount of data on adolescent drug use and determined that states where medical marijuana is now legal have seen no notable uptick in teen cannabis use.

The study was published in the medical journal The Lancet June 15. Ressearchers billed it as the most comprehensive report of its kind to date.

Scientists reviewed extensive survey data from the University of Michigan, which gathers yearly updates from American 8th, 10th, and 12th graders about their use of marijuana, alcohol, cigarettes, and other recreational drugs.

The researchers concluded that cannabis use among teenagers was higher than average in states that have adopted medical marijuana. But the difference had nothing to do with MMJ: The numbers were higher in these states even before medical legalization.

In other words, states that already enjoyed marijuana were the most likely to adopt it for medicinal use. This makes sense: Convincing a state full of stoners to support MMJ is a lot easier than convincing a bunch of NASCAR fans.

Teen marijuana use didn’t rise with MMJ

But the key finding of the Lancet study was that the higher use rates in cannabis-friendly states didn’t climb after the enactment of MMJ.

The study covered data gathered from more than 1 million adolescents over a quarter century, starting five years before the 1996 legalization of medical pot in California. In the time since that law passed, 36 other states have adopted MMJ; four of them now also allow recreational marijuana use.

Scientists examined statistics from 48 states and focused only on MMJ. They said they plan to examine underage recreational use next.

It’s still not entirely clear what happens when minors smoke marijuana. Some limited studies suggest that early, frequent use could stunt intellectual growth and cause permanent brain defects. At least some research indicates IQ levels may be lower in pot smokers who start young and use heavily.

Lack of scientific research

But there isn’t exactly a wealth of science on the subject. Researchers don’t know what causes these problems or exactly how they affect stoners, or even how problematic the problems are.

The uncertainty has led to a great deal of fear-mongering and panic among legalization opponents, mostly based on the slimmest of scientific evidence. Researchers wanted to provide some definitive answers.

The Lancet study isn’t the first to tackle questions of nationwide teenage drug use. Some earlier studies suggested an increase following MMJ, while others with slightly larger sample sizes found otherwise.

Reliable data

Marijuana TeenagerThis study, though, includes a huge sample size, far larger than most human studies are able to access. That means the results are likely much more accurate and reliable. Scientists behind the study said they hope their work will clear up some confusion in the public discourse.

“We have a war going on over marijuana, and I think both sides have been guilty at times of spinning the data,” said Dr. Kevin Hill, an assistant professor of psychiatry at Harvard University. “It’s nice to have a scientifically rigorous study to guide policy.”

Opponents of legalization predictably tried to cast doubt on the study, saying the period of time it covers – 24 years – somehow isn’t long enough to prove legalization won’t lead to increased adolescent pot smoking.

“Medical marijuana laws vary drastically across the U.S. and often take years to be implemented, so what we need to see is the longer-term effects of these laws and the accompanying commercialization efforts, which this study does not do,” said Kevin Sabet, a leading cannabis foe.

Overall, the study found that 16 percent of teens have used pot in states where it’s legal as medicine. Roughly 13 percent have tried the drug in other states. And the passage of MMJ laws made no apparent difference in either figure.

“We showed no hint of an increase at all after the laws were passed,” Dr. Hasin said.


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