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Study Shows Marijuana Use In Teens Correlates To Decreasing IQ 626

retroworks writes "The BBC reports on a paper published in the U.S.'s Proceedings of the National Academy of Sciences showing a correlation between persistent, regular cannabis use and risk of lower IQ. The study finds the risk particularly correlates use of cannabis by teenagers who use the drug "four times a week year after year." The more people smoked, the greater the loss in IQ. Reviewers of the study at King's College Institute of Psychiatry states that the data and methodology are exceptional, but she also cautions that there may be another explanation, such as depression, which could lower IQ while stimulating marijuana use. The study does not mention or rule out 'nocebo' effects, i.e. just feeling stupid for spending your teens hanging out with potheads."
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Study Shows Marijuana Use In Teens Correlates To Decreasing IQ

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  • by HungryHobo ( 1314109 ) on Tuesday August 28, 2012 @09:21AM (#41147603)

    Those who started after the age of 18 did not have the same IQ decline.

    "It's such a special study that I'm fairly confident that cannabis is safe for over-18 brains, but risky for under-18 brains."
    -King's College professor Terrie Moffitt.

  • Re:Work ethic... (Score:5, Informative)

    by Dr_Barnowl ( 709838 ) on Tuesday August 28, 2012 @09:46AM (#41147947)

    It demotivates you. I've lived with stoners and they were some of the most lackadaisical folks I've met. If you're not going to get up off your ass and get a job, and prove that you want to keep it, you're not going to be employed, simple as that.

    My POV on the IQ loss is that there's probably a heavy component of just not exercising the mind, because you can't be bothered.

  • Re:News Flash (Score:2, Informative)

    by assertation ( 1255714 ) on Tuesday August 28, 2012 @09:48AM (#41147965)

    I agree 100%, but if you have ever listened to marijuana activist talk their message tends to be that ANYTHING less than 100% positive written about marijuana is a LIE by the powers that be.

  • Re:Confounding (Score:5, Informative)

    by stranger_to_himself ( 1132241 ) on Tuesday August 28, 2012 @09:55AM (#41148059) Journal

    It was a longitudinal study. First assessment was before anybody had smoked anything, and it was the change in IQ that was tracked.

  • by udachny ( 2454394 ) on Tuesday August 28, 2012 @09:57AM (#41148105) Journal

    (same guy here, my first account is limited because of trolls, like you)

    That's good, because I come from a fairly rich family and - since it's not a governmental issue - I can just take over the land I want.

    - it's not a government issue, it's a private matter. Just because 'you come from a rich family' doesn't change that fact that government shouldn't be involved in private disputes of this type.

    That's good, because without group responsibility there is no government, and see above.

    - quite the contrary, there is no such thing as 'group responsibility', there is only individual responsibility. The very idea of 'group responsibility' should be immediately taken with all sorts of prejudice. Should you pay a fine for somebody else's transgressions? Should you be thrown to jail for somebody else's crime?

    Are not everybody paying for the other people's mistakes because of this ridiculous idea of 'group responsibility' at the very moment when the government steals from everybody to bail out the failed companies, like banks? What about all the subsidies that are given to corporations to do whatever they do, just because they have good access to the power in the government, isn't everybody made responsible 'as a group' for their behavior? You are a troll, though the moderators don't understand it.

    If you hit somebody with a car, it's a private matter. People don't need government to have working competing criminal and judicial systems.

    As to mass transit - the very concept of it was destroyed in USA with the government subsidizing the auto, gas and road building companies, when they stepped in to create that giant network of unprofitable (and thus unsustainable and unmaintainable in the long run) system of highways, that in reality was just a power grab and a huge heist.

  • Re:News Flash (Score:5, Informative)

    by WaywardGeek ( 1480513 ) on Tuesday August 28, 2012 @09:59AM (#41148147) Journal

    I noticed the article talked about people who kept on smoking pot until they were 35. I though I'd be a counter-example to this study, but I only smoked pot heavily in 9th grade. Before that I was universally called the "space cadet", and was infamous for getting lost on the way to the bathroom. I managed to get a D- in 8th grade, which is incredibly hard to do, especially in a school with low standards and easy teachers who hate giving F's. My IQ never tested particularly high as a kid. In 9th grade, I got all A's, and mostly A+'s. Going to school stoned was great. I even joyed spelling tests! By 10th grade, I'd smoked so much pot I burned out on it. I could get high just going for a jog. I gave it up and never started again. School was a lot harder while not stoned, but I still managed a respectable 3.85 average (9th - 12th, back when 4.0 was the max).

    My memory remains a leaky can, and I've wondered if smoking pot in 9th grade degraded it any. Thanks for the link to that article about pot improving memory. It does make me feel a bit better. I haven't been officially tested lately for my IQ, but on a dumb on-line quiz that my friends were all taking, I got 100% right, far higher than any of them, and most of them are pretty sharp. If there's a negative impact of heavy smoking for one year in the early teens, I don't know what it is.

  • Re:No surprise there (Score:3, Informative)

    by Anonymous Coward on Tuesday August 28, 2012 @10:04AM (#41148231)

    You do realize that we (the netherlands) have a much lower percentage of regular cannabis users than, say, the US, right?

  • Re:Confounding (Score:5, Informative)

    by radtea ( 464814 ) on Tuesday August 28, 2012 @10:11AM (#41148355)

    Does smoking pot as a teen lower your IQ, or are stupid teens more likely to smoke pot?

    From the abstract; "Impairment was concentrated among adolescent-onset cannabis users, with more persistent use associated with greater decline. Further, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users. Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain and highlight the importance of prevention and policy efforts targeting adolescents."

    A randomized controlled trial is by far the best means of proving causality, but a strong dose-response curve is a good secondary indicator. In this case, the data don't seem to support the contention of the abstract very well. Here they are from Table 1 in the paper:

    Persistence of regular cannabis use
    Never used | 242 | 38.84 | 99.84 (14.39) | 100.64 (15.25) | 0.05
    Used, never regularly | 508 | 50.59 | 102.27 (13.59) | 101.24 (14.81) | â'0.07
    Used regularly at 1 wave | 47 | 72.34 | 101.42 (14.41) | 98.45 (14.89) | â'0.20
    Used regularly at 2 waves | 36 | 63.89 | 95.28 (10.74) | 93.26 (11.44) | â'0.13
    Used regularly at 3+ waves | 41 | 78.05 | 96.00 (16.06) | 90.77 (13.88) | â'0.35

    Where the columns are: MJ usage category, # of people in category, %male, Avg(SD) IQ at 7- 13 years old, Avg(SD) IQ at 38 years old, size of effect.

    There are a couple of striking things: the percentage of males jumps markedly as the regularity of cannabis use goes up, and the initial IQ drops. So this study shows that young men with slighlty lower than average IQ are more likely to engage in regular cannabis use, and this may or may not result in a further decrease in their IQ over time.

    Also, the numbers in the regular use categories are quite small: a few dozen.

    I've not read the paper in detail, but superficially this looks exactly like the kind of research that led to hormone replacement therapy being touted as a good thing for post-menapausal women. Selection effects amongst the population of HRT users in the early days resulted in apparently dramatically improved health outcomes, whereas when applied to the general population the results were just the opposite.

    While the data are plausibly suggestive that cannabis is bad for the adolescent brain, it is also plausibly suggestive that the lower-IQ male adolescent is more at risk for cannibis use and IQ decline.

  • by betterunixthanunix ( 980855 ) on Tuesday August 28, 2012 @10:31AM (#41148687)

    Crystal Meth.

    Methamphetamine is already legal by prescription and it is prescribed to both children and adults. Most of the harm caused by recreational methamphetamine is caused by toxic byproducts that are left over from poorly controlled and completely unregulated production processes, which is a direct result of prohibition; such things are not present the pharmaceutical grade methamphetamine that doctors prescribe.

    Bath Salts.

    You will have to be more specific, since that is a generic name for a number of stimulants that are also produced under poorly controlled and unregulated conditions. Yes, the media has been playing up the risk, but the stimulant psychosis is not news, and incidents involving caffeine seem to go unnoticed (or do you really think coffee should be illegal?): []

    The difference, of course, is that caffeine pills come with dosage information, their production is regulated, and you know that they contain caffeine. "Bath salts" come with no such information, and you have no idea what they contain -- it might be MDPV, but it could just as easily be caffeine, some unknown byproduct of MDPV synthesis, or something that is only known among drug researchers. Do you see the pattern yet?


    PCP is legal by prescription (same schedule as methamphetamine), for use as a painkiller. Recreational users have the same problems as recreational methamphetamine users: poor production, unknown dosage, etc. There is not much more to be said -- the problem here is not the drug, it is the law.

  • Re:News Flash (Score:5, Informative)

    by mikael_j ( 106439 ) on Tuesday August 28, 2012 @10:39AM (#41148817)

    Actually no, the argument put forth by NeoMorphy is a classic fallacious argument that doesn't hold up well to scrutiny. It's used for pretty much anything that should be a personal choice that certain people have moral or ideological objections to. It can be summed up as "If you say something isn't harming you or that it isn't addictive then that is in itself a sign of harm or addiction and thus you voicing your opinion "proves" that it is harmful and addictive and any further protest from you merely demonstrates how hopelessly addicted you are". This argument is quite familiar to me as the rabid anti-drug crowd here in Sweden have been using it every chance they get for decades...

  • Re:News Flash (Score:5, Informative)

    by schlachter ( 862210 ) on Tuesday August 28, 2012 @10:45AM (#41148917)

    The pot smoking community has released their official response to this study, saying, "dude, chill with the anti pot stuff."

  • Re:News Flash (Score:2, Informative)

    by TemperedAlchemist ( 2045966 ) on Tuesday August 28, 2012 @11:05AM (#41149267)

    No. []

    You don't understand what you're talking about.

  • by Belial6 ( 794905 ) on Tuesday August 28, 2012 @12:11PM (#41150343)

    As someone else pointed out, it is entirely possible that sitting around doing nothing all day will lower IQ, and so marijuana's role may just be in discouraging teenagers from participating in activities that maintain or increase their IQ.

    I have always heavily suspected that this is the single biggest issue with "marijuana making you dumb". We see the same kinds of effects with people who have other, non-intellectual hobbies that they over indulge in. (sleeping, reading romance novels, playing sports, etc..., etc..., etc...) I'm pretty sure that we have some strong evidence that mental stimulation makes people smarter than they would be without it.

  • Re:Mods (Score:5, Informative)

    by composer777 ( 175489 ) * on Tuesday August 28, 2012 @12:24PM (#41150547)

    You should study the history of anti-drug research. One of the original studies that claimed marijuana caused severe brain damaged basically put face masks on monkeys and had them inhaling nothing but smoke for a significant period of time. The cause of the brain damage was CO poisoning and general hypoxia, which should have been obvious to anyone with half a brain. No one breathes nothing but smoke when they smoke. That's what a lot of studies do, they give a subject 100x the dose that is used, or use some unusual delivery method, and perform the study on it, drawing absurd conclusions that aren't event remotely scientific.

    The purpose? Funding, plain and simple. Studies that are anti-drug get lots of funding, and those that aren't, don't get approved (by the DEA when performed on humans) or funded. Why? Because the government funds the studies and the drug war is a political tool that they need evidence to support. A huge amount of science is shaped and steered through funding, and it absolutely biases the results.

    If you are reasonably intelligent, this shouldn't surprise you. We've had quacks for the entire history of science and medicine, and many of them have used science to explain what is clearly a politically motivated status quo. Just look at all the studies that assumed minorities were inferior, and proposed to find out why (by measuring brain volume and other anatomical characteristics), without first checking the assumption that minorities were inferior.

  • Re:News Flash (Score:5, Informative)

    by jasno ( 124830 ) on Tuesday August 28, 2012 @12:56PM (#41151045) Journal

    A telephone survey? Really?

  • Re:Mods (Score:4, Informative)

    by TheRealMindChild ( 743925 ) on Tuesday August 28, 2012 @01:05PM (#41151277) Homepage Journal
    No. First, let us look at this little tidbit:

    Having taken into account other factors such as alcohol or tobacco dependency or other drug use, as well the number of years spent in education...

    So there was manipulation of the data to exclude the effect of these "other factors", which completely throws out any correlation that these could/would/should have. It would be akin to testing if teen pregnancy lowered IQ, but they threw out data belonging to private school girls.

    they found that those who persistently used cannabis - smoking it at least four times a week year after year through their teens, 20s and, in some cases, their 30s - suffered a decline in their IQ.

    This is plain bad science. These people they are studying are CHRONIC users. They are likely using right up to the morning of their "interview". It is like the kid who started smoking cigarettes at 8 years old vs. someone starting at, say 23. The former is most likely to smoke 2+ packs a day. The latter usually smokes less than one pack. Also, nothing has been done to show what happens when they would stop.

    I get my data through observation of people throughout my life from all sorts of geography. I absolutely believe that my retort has as much of a proper sampling as 1000 people from New Zealand

"And remember: Evil will always prevail, because Good is dumb." -- Spaceballs