TUESDAY, July 9, 2019 (HealthDay News) -- Despite what many might think, legalizing marijuana does not encourage pot use among teenagers, and it may actually discourage them from smoking weed, a new study suggests.
Medical marijuana laws don't appear to influence teens' use of pot one way or the other, according to survey data from more than 1.4 million U.S. high school students.
And teen marijuana use actually seems to decline in states that have gone further and legalized recreational pot, researchers report online in the July 8 issue of the journal JAMA Pediatrics.
"There is simply no evidence that legalization -- for medical or recreational purposes -- leads to an increase in teen use," said lead researcher Mark Anderson, an associate professor of agricultural economics and economics at Montana State University. "Opponents of these laws generally state this as a primary concern, but there is just no evidence that teen consumption goes up."
Medical marijuana laws have been enacted in 33 states, while 10 states and Washington, D.C., have legalized the recreational use of pot, researchers said in background notes.
For the study, Anderson and his team analyzed responses to federal and state Youth Risk Behavior Surveys gathered between 1993 and 2017. These surveys track alcohol, drug and tobacco use among U.S. teens.
The researchers compared reported marijuana use among teenagers before and after pot legalization occurred in 27 different states and the District of Columbia.
They found that medical marijuana laws had no effect whatsoever on whether teens toked.
On the other hand, recreational pot legalization resulted in an 8% decrease in the odds of marijuana use and a 9% decrease in the likelihood a teen would become a frequent marijuana smoker.
"This could be due to the fact that it becomes relatively more costly to sell to teens post-legalization," Anderson said. "This result is consistent with the argument that it is more difficult for teens to obtain marijuana as drug dealers are replaced by licensed dispensaries that require proof of age."
These results jibe with information gained from other studies, Anderson noted.
For example, a December 2018 study found that pot use among younger teens in Washington state declined a small but statistically significant amount following the legalization of recreational marijuana in 2012.
Another study, published in February 2019, found that states with medical marijuana laws had 1.1% fewer teenage pot smokers than states without such laws.
"Our paper is the most recent in a now-growing literature that has come to the same conclusion," Anderson said.
But the picture isn't quite that clear, argues Pat Aussem, director of clinical content and development at the Center on Addiction.
"This study conflicts with other studies that have found that states that have passed recreational marijuana laws have experienced increases rather than decreases in adolescent marijuana use," Aussem said.
"For instance, the National Survey on Drug Use and Health reports both an increase in reported marijuana use and a decrease in the perceptions of risk associated with marijuana use among teens aged 12 to 17, compared to the national average," she said.
The 2018 Monitoring the Future survey discovered an increase in past 30-day pot use among the nation's teens, Aussem added.
Kids who experiment with pot could be doing long-term damage to their brain, she said.
"Marijuana use interferes with the developing adolescent brain and can create problems with critical thinking skills, impair reaction time and coordination, and increase the risk of developing other mental health disorders," Aussem said. "When teens and young adults use marijuana, they are nearly twice as likely to develop a cannabis use disorder as adults.
"It's our collective responsibility to ensure the mental health fitness of our young people against the landscape of legalization, proliferation of dispensaries, aggressive marketing efforts and the increase in THC potency," Aussem concluded. "They deserve nothing less."
The U.S. National Institute on Drug Abuse has more about marijuana use among teens.