Starting in 1996, Alexa Internet has been donating their crawl data to the Internet Archive. Flowing in every day, these data are added to the Wayback Machine after an embargo period. ||||| Teen use of marijuana doesn't seem to change when states pass laws legalizing the drug for medical purposes, a new study suggests. 
 
 Researchers analyzed information from more than 1 million U.S. teens in grades 8, 10 and 12, who were asked whether they'd used marijuana in the past month. The researchers collected 24 years' worth of survey data, spanning 1991 to 2014. 
 
 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. 
 
 But when researchers looked at marijuana use over time in the 21 states where medical marijuana was legal by 2014, they found no change in marijuana use after a medical marijuana law was passed, compared with before. About 16 percent of teens said they had used marijuana in the past month before a law was passed, compared with 15 percent who said the same after a law was passed. 
 
 Two earlier studies also found that marijuana use among teens did not increase following the legalization of medical marijuana, but these studies were smaller, conducted in just four to five states. 
 
 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. "Rather, up to now, in the states that passed medical marijuana laws, adolescent marijuana use was already higher than in other states," he said. [The Drug Talk: 7 New Tips for Today's Parents] 
 
 Some people have been concerned that legalizing medical marijuana could lead to an increased use of the drug among adolescents, because teens might view the drug as more acceptable or less harmful when such laws are passed. But the new study suggests that these concerns "seem unfounded," the researchers said. 
 
 "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. 
 
 Dr. Seth Ammerman, a clinical professor of pediatrics at Stanford University School of Medicine, who was not involved in the new study, called the findings "reassuring," because they show "if a state does put in medical marijuana laws, that that’s not going to significantly affect adolescent use." 
 
 The fact that states with legalized medical marijuana have higher teen marijuana use in general — both before and after laws were passed — could be because people in those states have a more liberal attitude toward the drug, Ammerman said. 
 
 The researchers noted that because the study looked at medical marijuana laws only, the findings do not address whether laws allowing the recreational use of marijuana would affect teen marijuana use, the researchers said. In addition, because some states in the study had only recently passed medical marijuana laws, the analysis should be repeated after more years of data have been collected, the researchers said. 
 
 Other studies suggest that laws that legalize marijuana may increase the risk of marijuana exposure in very young children, who may accidentally swallow edible forms of marijuana. A study published earlier this month found that, in states that legalized marijuana between 2000 and 2013, the rate of marijuana exposure among children ages 5 and younger increased about 16 percent each year. 
 
 Earlier this year, the American Academy of Pediatrics issued a statement opposing use of marijuana for medical purposes, except for drugs that are approved by the Food and Drug Administration. The main concern with medical marijuana is that it is not standardized, so the term really applies to any part of the Cannabis plant, Ammerman said. 
 
 Until the compounds in marijuana go through the same approval process that other drugs go through, where they are required to show risks and benefits, "it's hard to recommend it," Ammerman said. 
 
 Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science. ||||| 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. 
 
 Since 1996, 23 US states and the District of Columbia (DC) have approved the medicinal use of cannabis. In the states of Colorado, Washington, Alaska and Oregon and DC, recreational use is also legal. These moves towards permissiveness, even where possession of the drug is restricted to medical use, have caused many critics to worry that cannabis use would rise, especially among teenagers. 
 
 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. However, the findings from 24 years of data from more than one million adolescents in the 48 contiguous states did not substantiate those fears. Their paper in the journal Lancet Psychiatry says that the use of cannabis by adolescents was already higher in the states that have opted for medical legalisation. But the change in the law did not lead to a jump in numbers. 
 
 Analysing data from a national study called Monitoring the Future, which collects information from 50,000 pupils aged 13 to 18 in the 8th, 10th and 12th grade (years 9, 11 and 13 in Britain) every year, they found there had not been a rise even after taking into account individual, school and state-level factors that can affect marijuana use (such as age, ethnicity, public or private school and proportion of each state’s population that was male or white). 
 
 “Our findings provide the strongest evidence to date that marijuana use by teenagers does not increase after a state legalises medical marijuana,” said Dr Hasin. “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. The authors speculate that the older students’ views on the drug may already have been fixed before medical legalisation, but that those who were younger were less likely to view it as recreational once medicinal use was authorised. Another possibility is that parents were taking a more vigilant and robust stance against it, the authors said, adding that this warranted further investigation. 
 
 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. “Hasin and colleagues postulated, as many would, that the passage of medical marijuana laws would increase adolescent marijuana use by contributing to the declining perception of the potential harms of marijuana. Their well-designed, methodologically sound study showed that this was not the case,” he says. 
 
 The study shows how important it is to test out hypotheses with rigorous research before making health policy, he says. “The growing body of research that includes this study suggests that medical marijuana laws do not increase adolescent use, and future decisions that states make about whether or not to enact medical marijuana laws should be at least partly guided by this evidence.” 
 
 David Nutt, professor of neuropsychopharmacology at Imperial College London, said the result of the study was as he would have predicted. “The illegal market for cannabis is probably saturated, so making it a medicine will just allow law-abiding citizens with chronic medical problems to obtain the relief ‎they have been denied for the past 40 years of prohibition,” he said. 
 
 British experts campaigning to reschedule cannabis in the UK to allow medicinal and research use welcomed the study. “Patients are suffering unnecessarily and others in great pain are travelling abroad to find the cannabis they need to ease their symptoms,” said Prof Val Curran of University College London, the UK’s leading expert on medicinal cannabis and joint author of a new report for the all-party parliamentary group for drug policy reform. “All this could change by moving cannabis from schedule 1 to schedule 2, thus recognising the medicinal value of the drug.” ||||| One of the biggest worries about legalized medical marijuana was that teenagers would smoke more pot, but it turns out those fears were wrong. A study just published in The Lancet Psychiatry showed no significant difference in adolescent marijuana use in the 21 states with medical marijuana laws. 
 
 This exhaustive study using over 24 years of data from over a million teenagers in 48 states found no evidence that legalized medical marijuana led to teenagers using pot more. Deborah Hasin, Professor of Epidemiology at Columbia University Medical Center in New York, reviewed data on teenagers between the ages of 13-18 and during the years 1991-2014. “Our findings provide the strongest evidence to date that marijuana use by teenagers does not increase after a state legalizes medical marijuana. Rather, up to now, in the states that passed medical marijuana laws, adolescent marijuana use was already higher than in other states. 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 priority,” said Dr. Hasin. 
 
 This study supports the 2013 report from the Colorado Department of Health and Environment that found that high school marijuana use decreased from 22% in 2011 to 20% in 2013. The data was collected before recreational marijuana was made legal, but it did demonstrate that legalizing medical marijuana did not send the message that it was okay to use. Dr. Larry Wolk, the CDPHE director said, “As with tobacco, youth prevention campaigns will help ensure adult legalization of marijuana in Colorado does not impact the health of Colorado kids.” 
 
 In California where medical marijuana has been legal for many years in an unregulated environment, marijuana use in teens has remained less prevalent than the years before the marijuana was legal according to results from the 13th Biennial California Student Survey. Stepping back to 2012, a study entitled, “Medical Marijuana Laws and Teen Marijuana Use” by D. Mark Anderson, Ben Hanson and Daniel Rees did not find that legalizing medical marijuana increased pot use in teens. They actually found that during the time period they collected data, pot use increased among teens, but not in the states where medical marijuana was legal. 
 
 In a linked comment to the study by Dr. Hasin, Dr. Kevin Hill of McLean Hospital's Division of Alcohol and Drug Abuse said, “The growing body of research that includes this study suggests that medical marijuana laws do not increase adolescent use and future decisions that states make about whether or not to enact medical marijuana laws should be at least partly guided by this evidence. The framework of using a scientific method to challenge what might be ideological beliefs must remain an important driver of future research on marijuana policy.” 
 
 Organizations that are against legalizing medical marijuana like Smart Approaches to Marijuana cite a report from Monitoring the Future by the University of Michigan that says access to pot has increased and usage is up. The report, a National Survey on Drug Use, instead notes that pot use cycles up and down amongst teens and that it has actually dropped in 2013-2014. 23% of teens use marijuana now as compared to 36% in 1979. 
 
 This report points out the marijuana has been the consistently most available illicit drug since 1975 where 81% of teens said they could get it,moving up to 90% now. However, being about to get it and wanting to use it are two different things. The report said, “In 2014 marijuana use showed a one-year, slight decline in lifetime, annual, thirty-day, and daily use in all three grades. 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. That certainly doesn't fit with the idea of being a rebellious teenager. Adults thinking that smoking pot is cool could be the easiest way to keep to teens from smoking it.
– 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.)