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  1. #1
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    Does Marijuana Use By Teens Cause a Drop in IQ?

    Teenage pot smoking tied to loss of IQ
    CBC News
    Aug 27, 2012

    Teens who smoke marijuana regularly may suffer long-term damage to their brains, new research suggests.

    Age of onset for cannabis use and brain development seems to be key, said lead researcher Madeline Meier, a post-doctoral researcher at Duke University in Durham, N.C.

    The researchers looked at how IQ scores changed between ages 13 and 38 in more than 1,000 participants from New Zealand who were born in in 1972 and 1973 and followed until age 38.

    The key variable was the age of onset for marijuana use and the brain's development, Meier said.

    Before the age of 18, the brain is still being organized and is thought to be be more vulnerable to damage from drugs.

    Persistent cannabis use appeared to affect everyday cognitive functioning, with persistent users showing more attention and memory problems than other participants, the researchers reported in Monday's online issue of the PNAS.

    About five per cent of the study group were considered marijuana-dependent, or were using more than once a week before age 18. A dependent user is one who keeps using despite significant health, social or family problems.

    The participants had tests including memory, reasoning and processing speed.

    IQ scores dropped only in those who became dependent by age 18, the researchers found.

    The scores dropped by an average of eight points among those considered dependent in three or more surveys.

    For someone of average intelligence, an eight-point drop would mean ranking higher than 29 per cent of the population instead of 50 per cent, Meier said.

    Earlier studies did not measure brain function before marijuana use began.

    "I think this is the cleanest study I've ever read" that looks for long-term harm from marijuana use, said Dr. Nora Volkow, director of the U.S. National Institute on Drug Abuse, which helped fund the research along with the British government, and a foundation in Zurich.

    Ken Winters, a psychiatry professor at the University of Minnesota and senior scientist at the Treatment Research Institute in Philadelphia, said the new findings aren't definitive, but they underscore the importance of studying how marijuana may harm young people. He had no role in the work.

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    Teenage pot smoking may lower IQ ? for life

    Teenage pot smoking may lower IQ – for life
    by Zosia Bielski, The Globe and Mail
    Monday, Aug. 27 2012

    Chronic use of the chronic before age of 18 can cause “lasting harm to a person’s intelligence, attention and memory” – and quitting pot later in life doesn’t reverse the damage, says daunting new research out of New Zealand.

    The study, which followed 1,037 Kiwis for nearly 40 years, found that adolescents who smoked marijuana persistently for years showed declines of eight IQ points when their scores were tabulated at age 13 and then at 38. Teens who got stoned regularly all scored significantly worse than their sober counterparts on tests measuring memory, reasoning and processing speed, with family and friends of users corroborating the findings anecdotally.

    “Marijuana is not harmless, particularly for adolescents,” lead researcher Madeline Meier, a post-doctoral researcher at Duke University, said in a release. “Somebody who loses eight IQ points as an adolescent may be disadvantaged compared to their same-age peers for years to come.”

    Adolescent tokers are particularly vulnerable to lasting mental deficits because their brains are still developing, the researchers explained. Subjects who didn’t hit the bong until they were adults “with fully-formed brains” did not exhibit these drastic mental declines.

    (Approximately five per cent of the respondents were deemed “marijuana-dependent,” that is, lighting up more than once a week before turning 18. The researchers controlled for other drug and alcohol use and disparities in education.)

    What isn’t clear from this study is what quantity of weed causes damage, and what age (if any) might be safe for regular use.

    Marijuana use is up among American teens, who are now more likely to smoke pot than tobacco, according to a 2011 University of Michigan study.

    That study found one in every 15 high-school seniors getting high on a daily or near daily basis, the most substantive rates seen since 1981. One hypothesis for the resurgence is that teens perceive few risks associated with the drug, with many refusing to even call it a drug.

    In Canada, the prevalence of pot use among Canadians aged 15 and over decreased to 9.1 per cent in 2011 from 10.7 per cent in 2010.

    Still, the rates for youth aged 15 to 24 were three times higher than for their over-25 counterparts: 21.6 per cent versus 6.7 per cent.

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    Does Weekly Marijuana Use By Teens Really Cause a Drop in IQ?

    Does Weekly Marijuana Use By Teens Really Cause a Drop in IQ?
    By Maia Szalavitz, Time Magazine
    August 28, 2012

    A new study suggests marijuana use could have an impact on America's IQ, but how great is the effect?

    Heavy marijuana use is associated with cognitive decline in about 5% of teens, according to a new study, which suggests that the heaviest users could lose 8 IQ points.

    In the report, published in the Proceedings of the National Academy of Sciences, research conducted in New Zealand showed that teens who started smoking marijuana before age 18 and were diagnosed as being addicted to cannabis by age 38 experienced an IQ drop in early adulthood. But users who began smoking after age 18?even if they used heavily? did not show a significant decline.

    ?The effect of cannabis on IQ is really confined to adolescent users,? says lead author Madeline Meier, a postdoctoral researcher at Duke University, ?Our hypothesis is that we see this IQ decline in adolescence because the adolescent brain is still developing and if you introduce cannabis, it might interrupt these critical developmental processes.?

    The authors followed 1037 children born in the town of Dunedin, New Zealand in 1972 and 1973, virtually every child. They defined adolescent use as at least weekly use before turning 18. In looking at the relationship between marijuana use and IQ, they controlled for factors like years of education, schizophrenia and use of alcohol or other drugs that might also have an effect on IQ. While education weakened the relationship, it still did not eliminate it.

    Researchers also had family members and friends of the participants confidentially rate them on attention and memory skills and those who had lost IQ points showed problems in these areas. Meier notes that an 8 point decline in IQ for someone with average intelligence (an IQ score of 100; the 50th percentile) would move that person down to the 29th percentile. ?It?s fairly substantial but it does depend on where you start out,? she says.
    ?I think this is the cleanest study I?ve ever read? exploring the long term effects of marijuana use, Dr. Nora Volkow, director of the National Institute on Drug Abuse, told the Associated Press.

    ?The overall implication is that when you?re talking about marijuana, you have to take into account age of onset of use and dealing with developing, growing brains,? says Meier.

    Not all experts agree, however. ?Scientifically, these are extremely preliminary findings,? cautions Carl Hart, associate professor of psychology at Columbia University, who has studied the cognitive effects of marijuana in humans in the lab and was not associated with the research. (Disclosure: he and I are working on a book project together).

    Hart notes that because only 38 people in the study? around 8% of those who ever tried marijuana? used it heavily enough to get diagnosed with dependence during several follow-up periods, he is skeptical about how generalizable the results are. He says that in his studies of people who smoke at least three times a week, ?When you compare these people?s scores to a normative database on a wide range of domains including executive function, memory, and inhibitory control, they score dead smack in the middle, in the 50th percentile.?

    He explains, ?They are normal when not intoxicated. We test them when they are not intoxicated and when they are intoxicated. When they are intoxicated, there is some slowing of certain cognitive acts, but their accuracy doesn?t not change.? The New Zealand study, for example, did not identify whether the participants are employed or whether they are able to function in their families, which would be an important indicator of whether the drop in IQ has any real world impact.

    There are also other factors?such as child abuse or other trauma ?that might lead people to seek escape in heavy marijuana use and could also affect brain function. Meier and her colleagues did not examine these factors but say it?s possible that such elements could explain the results better than marijuana itself.

    If the link is real, the effects on cognition could be dramatic. But intelligence and cognition is affected by a plethora of other factors, including genetic, social and environmental influences that may supersede any influence from drug use. Despite the fact that the average marijuana user starts at age 17 in the U.S and nearly 7% of high school seniors currently smoke pot every day, IQ scores have risen tremendously over time in all developed countries in recent years. Most of those same countries also experienced a massive increase in marijuana use between the 1950s and today.

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