"Our study findings suggest that the debate over the role of medical marijuana laws in adolescent marijuana use should cease, and that resources should be applied to identifying the factors that do affect risk," the researchers wrote in the June 16 issue of the journal The Lancet Psychiatry.  Data on one million teenagers shows marijuana use did not increase in US states where it was legalised, with fall among youngest children, authors of study find 
 
 Legalising the medical use of cannabis has not led to a surge in the numbers of adolescents using it in the USA, according to new research that surprised its authors and will encourage those hoping for relaxation of the law elsewhere. That assumption was the starting point for the research carried out by Dr Deborah Hasin, professor of epidemiology at Columbia University Medical Center in New York, and her colleagues. The new findings "provide the strongest evidence to date that marijuana use by teenagers does not increase after a state legalizes medical marijuana, study co-author Deborah Hasin, a professor of epidemiology at Columbia University Medical Center, said in a statement. Overall, teen marijuana use was more common in states that had passed medical marijuana laws as of 2014 — nearly 16 percent of teens in states where medical marijuana is legal said they had used marijuana in the past month, compared with 13 percent of teens in states where medical marijuana is not legal. “Rather, up to now, in the states that passed medical marijuana laws, adolescent marijuana use was already higher than in other states.” 
 
 That still gave cause for concern, she suggested: “Because early adolescent use of marijuana can lead to many long-term harmful outcomes, identifying the factors that actually play a role in adolescent use should be a high research priority.” 
 
 Among the youngest students surveyed, the 8th graders, marijuana use actually dropped. In a commentary in the journal, Dr Kevin Hill, from the division of alcohol and drug abuse at McLean Hospital in Belmont, Massachusetts, writes: “Perhaps the main concern of many people opposed to medical marijuana laws is that they will lead to increased general marijuana use, including among adolescents.” 
 
 Cannabis use has increased in the US among teenagers in recent years, unlike nicotine, alcohol or opioids, and the perception of its dangers has dropped, he points out. This finding is unexpected in light of the positive publicity marijuana has received in recent years prior to the data collection in 2014, with several states allowing medical marijuana use and two states (Colorado and Washington) legalizing recreational use for adults.” 
 
 The report goes on to speculate that legalizing medical marijuana could send the signal to teens that the drug isn't dangerous and probably won't be very harmful.
– A big boost for medical marijuana advocates: A massive study involving data on a million teenagers in 48 states has found no evidence that legalizing pot for medical use does anything to increase teen usage, the Guardian reports. The study, published in the Lancet Psychiatry journal, looked at some 1,098,270 8th-grade, 10th-grade, and 12th-grade students over 24 years; the teens had been asked if they used pot in the last 30 days. The researchers found that teenage pot use not only failed to rise in the 21 contiguous states where medical marijuana was legalized as of 2014 (Alaska and Hawaii bring the nation's total to 23), usage actually went down among the youngest teenagers, from about 8% before the law was passed to 6% after. In states that brought in medical marijuana laws, teen pot use was already slightly higher than in other states, at about 16% usage to 13%. Experts say that could be due to a more liberal general attitude toward the drug, LiveScience reports. "Our study findings suggest that the debate over the role of medical marijuana laws in adolescent marijuana use should cease, and that resources should be applied to identifying the factors that do affect risk," the researchers wrote. As for why pot use fell among 8th graders after it was legalized for medical purposes, here's one theory: that the teens started to see marijuana as a relatively harmless medical product, which "certainly doesn't fit with the idea of being a rebellious teenager," writes Debra Borchardt at Forbes. (A separate study tracked the pot "use" of kids—under age six.)