The enactment of state medical marijuana laws doesn't increase teen use of the cannabis plant, according to an exhaustive study published Tuesday by Columbia University researchers in The Lancet Psychiatry.
Researchers looked at over 24 years of data from more than 1 million teenagers in 48 states, and found no evidence that legalized medical marijuana resulted in teenagers using more.
"The risk of marijuana use in states before passing medical marijuana laws did not differ significantly from the risk after medical marijuana laws were passed," the authors wrote.
Opponents of medical marijuana often claim that legalization will result in increased use, but lead author Deborah Hasin, a researcher at Columbia University in New York, described the findings as "the strongest evidence to date that marijuana use by teenagers does not increase after a state legalizes medical marijuana," reported Forbes.
While the study found no noticeable spike in use in the 21 states that had legalized medical marijuana, researchers did find that usage rates were usually higher in states with medical marijuana, but noted that marijuana use already tended to be higher in those states before legalization.
"State-level risk factors other than medical marijuana laws could contribute to both marijuana use and the passage of medical marijuana laws, and such factors warrant investigation," the researchers said.
The researchers also saw a significant decline in marijuana use by 8th graders after passage of medical marijuana laws, and speculated that the laws could have caused the students to be less likely to view marijuana as a recreational drug. No significant change was found in 10th or 12th- graders' use.
To reach their conclusions, researchers analyzed responses from 8th, 10th and 12th graders who had completed an annual government-funded survey asking about marijuana use in the previous month.
