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Cannabis more damaging to under-18s, study suggests

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First convincing evidence that cannabis has a different effect on young brains than on those of adults

http://www.guardian....under-18s-study

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Cannabis is not harmless, particularly for adolescents, the researchers say. Photograph: Gareth Fuller/PA

Adolescents who are regular users of cannabis are at risk of permanent damage to their intelligence, attention span and memory, according to the results of research covering nearly four decades.

The long-term study which followed a group of over 1,000 people from birth to the age of 38 has produced the first convincing evidence, say scientists, that cannabis has a different and more damaging effect on young brains than on those of adults.

Around 5% of the group used cannabis at least once a week in adolescence or were considered dependent on it. Between the age of 13 and 38, when all members of the group were given a range of psychological tests, the IQ of those who had been habitual cannabis users in their youth had dropped by eight points on average.

Giving up cannabis made little difference – what mattered was the age at which young people began to use it. Those who started after the age of 18 did not have the same IQ decline.

"This work took an amazing scientific effort," said Professor Terrie Moffitt of King's College London's Institute of Psychiatry, one of the authors.

"We followed almost 1,000 participants, we tested their mental abilities as kids before they ever tried cannabis, and we tested them again 25 years later after some participants became chronic users.

"Participants were frank about their substance abuse habits because they trust our confidentiality guarantee, and 96% of the original participants stuck with the study from 1972 to today.

"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."

The research, on people in Dunedin, New Zealand, was carried out by researchers from King's College and Duke University, North Carolina in the United States and published online by PNAS (Proceedings of the National Academy of Sciences).

"Marijuana is not harmless, particularly for adolescents," said Madeline Meier from Duke, one of the researchers. While eight IQ points on a scale where the mean is 100 may not sound a lot, she said, a drop from 100 to 92 represents a move from the 50th to the 29th percentile. Higher IQs correlate with higher education and income, better health and a longer life.

"Somebody who loses eight IQ points as an adolescent may be disadvantaged compared to their same-age peers for years to come," Meier said. The study took into account the education of the participants, which can be disrupted by drug use.

The authors say that young people tend today to think that cannabis is harmless. "Increasing efforts should be directed toward delaying the onset of cannabis use by young people, particularly given the recent trend of younger ages of cannabis-use initiation in the United States and evidence that fewer adolescents believe that cannabis use is associated with serious risk," says the paper.

"The simple message is that substance use is not healthy for kids," said Avshalom Caspi, of Duke and King's, one of the leaders of the study. "That's true for tobacco, alcohol, and apparently for cannabis."

Robin Murray, professor of psychiatric research at King's, who was not involved in the study, said the paper was impressive and if the same results were found in other research, public education campaigns should be launched to warn of the dangers of cannabis to younger people. "The Dunedin sample is probably the most intensively studied cohort in the world and therefore the data is very good. The researchers, who I know well, are among the best epidemiologists in the world. Therefore, although one should never be convinced by a single study, I take the findings very seriously.

"There are a lot of clinical and educational anecdotal reports that cannabis users tend to be less successful in their educational achievement, marriages and occupations. It is of course part of folklore among young people that some heavy users of cannabis seem to gradually lose their abilities and end up achieving much less than one would have anticipated. This study provides one explanation as to why this might be the case."

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just once i'd like to see a mainstream newspaper contain, if not a link to the abstract then at least list the study name/journal. v. frustrating.

"Somebody who loses eight IQ points as an adolescent may be disadvantaged compared to their same-age peers for years to come," Meier said. The study took into account the education of the participants, which can be disrupted by drug use.

it's fairly well established now that IQ doesn't have as big an impact on success as previously thought. besides, the measure of iq in itself is a flawed measure of intelligence, imo. anyway seems good, the simple message i guess is "kids: say no to drugs. adults: smoke up!"

Edited by qualia
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"Persistent cannabis users show neuropsychological decline from childhood to midlife

  1. Madeline H. Meiera,b,1,
  2. Avshalom Caspia,b,c,d,e,
  3. Antony Amblere,f,
  4. HonaLee Harringtonb,c,d,
  5. Renate Houtsb,c,d,
  6. Richard S. E. Keefed,
  7. Kay McDonaldf,
  8. Aimee Wardf,
  9. Richie Poultonf, and
  10. Terrie E. Moffitta,b,c,d,e

  1. [/url] aDuke Transdisciplinary Prevention Research Center, Center for Child and Family Policy,
  2. bDepartment of Psychology and Neuroscience, and
  3. cInstitute for Genome Sciences and Policy, Duke University, Durham, NC 27708;
  4. dDepartment of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, NC 27710;
  5. eSocial, Genetic, and Developmental Psychiatry Centre, Institute of Psychiatry, King’s College London, London SE5 8AF, United Kingdom; and
  6. fDunedin Multidisciplinary Health and Development Research Unit, Department of Preventive and Social Medicine, School of Medicine, University of Otago, Dunedin 9054, New Zealand

Abstract

Recent reports show that fewer adolescents believe that regular cannabis use is harmful to health. Concomitantly, adolescents are initiating cannabis use at younger ages, and more adolescents are using cannabis on a daily basis. The purpose of the present study was to test the association between persistent cannabis use and neuropsychological decline and determine whether decline is concentrated among adolescent-onset cannabis users. Participants were members of the Dunedin Study, a prospective study of a birth cohort of 1,037 individuals followed from birth (1972/1973) to age 38 y. Cannabis use was ascertained in interviews at ages 18, 21, 26, 32, and 38 y. Neuropsychological testing was conducted at age 13 y, before initiation of cannabis use, and again at age 38 y, after a pattern of persistent cannabis use had developed. Persistent cannabis use was associated with neuropsychological decline broadly across domains of functioning, even after controlling for years of education. Informants also reported noticing more cognitive problems for persistent cannabis users. 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."

http://www.pnas.org/content/early/2012/08/22/1206820109.abstract?sid=86ce4136-6712-4372-bac6-280ac41c6f79

Apparently the full paper will be available for free in 6 months, unless someone has a subcription?

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"Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain and highlight the importance of prevention and policy efforts targeting adolescents."

Fair enough. I wish I didn't start smoking cannabis when I was 14. This sort of info just wasn't available back then. Just murmurs of psychosis in predisposed individuals (usually from nurses and health professionals).

Edited by tedzr

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Sif reading a study like that would have any impact on a 14 year old's reasoning for why they're smoking weed :P

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I guess that's the weakness of seriously long-term longitudinal studies - the testing methods are 40 years out of date by the time it's finished.

But bloody IQ testing - really? - the problems with those tests were known in 1972, weren't they? A big problem which may be relevant to these results is the fact that there is often only one "correct" answer, which assumes a certain level of knowledge and reasoning. This makes it possible to over-think the questions and come up with an answer that is equally "correct", and would probably be marked correct if you were asked to explain your reasoning, but the testers don't ask, so it just gets marked down as a wrong answer.

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I think most people who use cannabis habitually are essentially self medicating themselves. ESP adolescents. Society needs to address the cause of this not the symptoms.

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Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain

This is the main part I disagree with. There is not non-ambiguous evidence (aka the only kind of evidence) of a neurotoxic effect. Furthermore, what mechanism do they propose for its neurotoxic effects to disappear once those adolescents pass the magic threshold and become adults?

I feel rather certain that it's just indicative of a harmful attitude taking root, and that the attitude is "learning doesn't matter" or some paraphrase thereof. The younger you are when this attitude takes hold, the more crucial are the things that you miss. And to use the damn skyscraper metaphor again, if you miss a floor in the skyscraper of knowledge, all the higher floors will eventually disappear. Thus the younger you are when you miss a floor (via having an at-best indfferent attitude towards learning), the lower the level your knowledge plateau at. <- Here's your plausible mechanism right here.

This is functionally different to brain damage (which they're implicitly identifying as the likely cause of the IQ disparity), because re-learning the knowledge from the bottom up I'm very sure, will allow that individual to reach his/her statistical IQ with enough hard work. They have not even considered this possibility, probably because it shifts the onus of error from the cannabis plant onto the user for allowing themselves to stagnate their brain.

I feel that this study will likely become a landmark study if it hasn't already, and as a result, it's very important for us to deeply probe what it means, and what it does not.

Edited by CβL
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just a small sidetrack...

i noticed over the years, what seems to suggest, that cannabis has aswell a different effect onto the brain of say, a genius.

different to the effect that mensa people do get stoned and impared, but still seem to keep it up pretty well, in short they seem to function more "normal" than non mensa people.

Edited by planthelper

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When I was studying at college I took my first IQ tests in secret (because mensa people piss me off) and I was horrified, after 3 tests, to get no more than 86 on each test, one I got 84! I was sure I was a bit smarter than average (at least, that's what my parents and teachers said) so I became very suss about IQ tests. There were certain things on those tests I just couldn't do, esp. the maths, whereas other things I didn't have to think about. Years later, a mensa friend confided that he had always had a high IQ but by understanding and practicing the tests he had increased his IQ so that he was one of the top people in the country. So one day I went back and did some more tests, getting over 130 each time, sometimes a lot higher.

But I still don't know quite what an IQ test is or how it works, but it is clear they are able to be fudged, faked, fiddled, foxed and fucked quite nicely by whoever happens to be using them.

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Can dyslexics do IQ tests or do they have special ones designed for non-spellers? And can you be numerically dyslexic like I sometimes am particularly after becoming intoxicated?

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But I still don't know quite what an IQ test is or how it works, but it is clear they are able to be fudged, faked, fiddled, foxed and fucked quite nicely by whoever happens to be using them

yeah practicing iq tests increases your score dramatically, i think. i was able to increase my score by 20 just by practicing one of those "culture fair" tests 3 times.

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Can dyslexics do IQ tests or do they have special ones designed for non-spellers?

There are some tests which are done by verbally asking the questions (rather than giving you a test paper), at least for young kids who don't read well. Presumably this is what they'd do for anyone with reading/writing difficulty.

And yeah, about practice tests - the more cynical psychologists claim that the only thing that IQ tests measure well, is your ability to take IQ tests.

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i haven't done an iq test for a long time, but i remeber that i had quite a few dyslexic problems with the test.

so no ther is no iq test for dyslexics.

my dyslexia can vary, and very, very rarely, if i feel super well inside my brain, it seems not to be there.

my german tests, for example i would always fail, because of spelling mistakes, but the teacher loved my writting style.

i noticed that, if i get asked, a word, i do less mistakes, than for myselfe.

all i could do, to survive, is copy to from my neighbour, often, i spotted a mistake in his spelling, and corrected it, but i myselve wrotte it wrong....

Edited by planthelper

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There are some tests which are done by verbally asking the questions (rather than giving you a test paper), at least for young kids who don't read well. Presumably this is what they'd do for anyone with reading/writing difficulty.

And yeah, about practice tests - the more cynical psychologists claim that the only thing that IQ tests measure well, is your ability to take IQ tests.

that fixes only part of the problem.

dyslexic problems i remeber from the iq test, were that, i could not seperate mirror images, left or right.

for example dyslexics often don't know, in which direction to turn on or off water (specialy bad if the water is on already, and they want to adjust just the temperature, between cold and warm!!).

Edited by planthelper

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one more thing, i remeber now, regarding iq test and being dyslexic.

if the dyslexia get's strong, there is a certain sensation, in the head, and sometimes the letters seem to dance and move. i had this feeling with some aspects of the iq test.

in short iq tests definately discriminate against dyslexicis.

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Need to hear more about how the study was constructed, but arriving at 'suggestive of neurotoxicity' from this kind of study sounds to me like it is is really overreaching, especially when other studies strongly suggest Cannabis has neuroprotective properties and may even be a catalyst for neurogenesis.

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USE or ABUSE

same with anything, can be a fine line sometimes.

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I wonder what the conclusions of the study had been if instead of an IQ test the participants were asked to construct a piece of art? essentially what this study shows is that use of cannabis makes people less valuable to the materialist dominator culture. this is why the powers at be will fight tooth and claw to prevent legalisation, even more so for cannabis than psychedelics. maybe i should used cannabis when an adolescent, then I wouldn't be such a reductionist bore.

Edited by kalika
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^^ That's pretty much what I was thinking last night as I went to bed, why not do a study on the positive aspects of Cannabis use? The negative aspects seem so trivial, somehow, and extremely difficult to define. It took years of scientific effort to come up with results that are so easily disputed, yet the negative effects of alcohol misuse are so clear and obvious it's just a case of adding up the numbers to see who's been affected, not how.

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Sounds to me like they are just preparing for it's legalization and they need a "justification" for an age restriction.

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At a glance I see evidence of what could be considered congruent with these findings walk past my house every day. They aren't quite dragging their knuckles on the ground but they aren't far from it.

But if I put the observations into context, I couldn't say it's 100% caused by cannabis use. There are many factors which could complicate the data, such as socio economics. People from the lower echelons of society tend to gravitate towards vocations that don't need much thought at all, let alone higher thought and reasoning on difficult problems, so their IQ fades with age anyway. If they had something more stimulating than a bong and a playstation maybe they could have scored much higher on an IQ test.

Look at Carl Sagan, he's been credited by some as one of the greatest thinkers of the last century and he actually credits a lot of his higher reasoning to marijuana use.

How much of this comes down to environment and stimulation ?

Then there's the outcast effect created because of the social stigma associated with marijuana use. If these people were nurtured properly who knows how they would have turned out.

One of my best mates was the school Dux and he is brilliant. He started smoking when he was ten, but his parents embraced it and used it as an opportunity to challenge him mentally whenever they noticed him stoned. Going to his house smashed for the first time was an experience I'll never forget. His dad made a habit of presenting paradoxes with apparent easy solutions, that in turn created problems. I still ponder some his questions to this day.

If your brain gets wired from an early age to be secretive and paranoid because of social implications surrounding your drug use of course you are going to grow up with problems. A brain in fear can't function properly, if that fear is removed then I say most of that research would be irrelevant.

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This survey didn't address what they did when they were stoned and to me that makes a world of difference. I have to admit I didn't start regular use until I was older than 18 but I started at 16. My marijuana use I have to admit has in my mind caused a surge of creativity and has opened up more doors than it has shut, for example I believe marijuana played a key role in my thinkings about nature and my connection with it which has made me feel more connected to the world and in turn happier. Same goes for my cousin over in NZ, he's absolutely brilliant. Got into Uni to study law and never once studied for his high school exams. In my opinion 'the next Einstein' will likely come from someone whose dabbled in certain types of drugs. The scientist of today reduces the art to this spiritless and dull world in which to describe they have to go through mountains and mountains of theoretical babble. I must be fair on science, it certainly has it's purpose and it's use as we'd not be anywhere near where we are today if it weren't for science. I love science but I do think they've missed the point on a few things which certain parts of the psychedelic experience could help get help with.

Plus IQ tests, as have been stated before, aren't the best measure of actual intelligence, I mean there are still to this day arguments on how to define intelligence yet they think that they can come up with a test for something that they can't even define :scratchhead:

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