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Teen cannabis use lowers IQ, despite claims to the contrary

A study published today in the scholarly journal PNAS questions the conclusion of a paper from last year that was widely seen as greatly strengthening the evidence that regular cannabis use beginning in…

Researchers found early and persistent cannabis users showed an eight-point decline in IQ compared to those who hadn’t used cannabis in this way. Jonah G.S.

A study published today in the scholarly journal PNAS questions the conclusion of a paper from last year that was widely seen as greatly strengthening the evidence that regular cannabis use beginning in adolescence and continuing throughout young adulthood causes a decline in IQ by the late 30s.

In the original study, co-author of this article Madeline Meier and her colleagues assessed changes in IQ and specific cognitive abilities between adolescence and the age of 38 in 1,037 New Zealanders. All the subjects were born in Dunedin in 1972 or 1973.

The researchers assessed IQ and other mental abilities at age 13 (before cannabis was first used) and again at age 38, and asked participants about their cannabis use throughout adolescence and young adulthood. They also collected other related data.

They found that early and persistent cannabis users showed an eight-point decline in IQ compared to those who hadn’t used cannabis in this way. More detailed analyses pointed to cannabis use being the most plausible explanation for the decline for a number of reasons.

First, the decline in IQ was largest in those who began using cannabis in adolescence and used it regularly throughout adulthood. This relationship persisted after the researchers statistically adjusted for other factors that may affect IQ (such recent cannabis use, alcohol, tobacco and other drug use, and schizophrenia).

Second, the IQ decline was not explained by the lower educational achievement among cannabis users. The same effects were found in cannabis users who finished high school, and the decline persisted after statistically controlling for educational level attained.

Third, there was some recovery in IQ if users quit. But it was limited in participants who started smoking cannabis in adolescence and had only stopped using for a year or more. There was no IQ decline in cannabis users who started in young adulthood and ceased 12 or more months before.

Fourth, key informants (friends and family who knew the study participants well) were much more likely to report that heavy and persistent cannabis users had problems with memory and attention than were key informants of those who had not used cannabis in this way.

But the article published today suggests an alternative explanation for these findings.

Its author, Ole Rogeberg, argues that the apparent impact of cannabis on IQ could be attributed to reasons unrelated to cannabis use if low socioeconomic status (SES) participants were more likely to start early and become persistent cannabis users, and if their IQ declined more rapidly, especially after they left school.

Rogeberg argues that the same decline in IQ would occur if the two above conditions were true, and if cannabis use had no effect on IQ. He suggests his hypothesis could be tested by conducting additional statistical analyses of the Dunedin data.

The authors of the original paper have done these analyses and their results don’t support Rogeberg’s hypothesis. First, they eliminated the effects of SES on IQ by only examining the relationship between cannabis use and IQ decline in children who came from middle-class homes. They found the same IQ decline in cannabis users who started in adolescence and persisted using into young adulthood within middle-class cannabis users.

And, they didn’t find any support for Rogeberg’s hypothesis that the IQ of low SES participants would be boosted by schooling and decline faster after they left school. Rather, Meier and her colleagues found that average IQs were unchanged in low SES participants between beginning school and adolescence. Most critically, low SES was not related to IQ decline between adolescence and young adulthood.

The paper published today by Rogeberg has raised a seemingly plausible alternative explanation for the finding of an IQ decline in early and heavy cannabis users – but analyses of the Dunedin study data do not support it. The most plausible explanation for the data remains that using cannabis from adolescence and into young adulthood contributes to a decline in cognitive ability, as indicated by performance on IQ tests.

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69 Comments sorted by

  1. Craig Minns

    Self-employed

    Seems logical, but far less significant than the cognitive impact of a lack of iodine in early development, which can be 15-30 points of IQ.

    It's fascinating that cannabis use is targetted, while we make no effort to address the chronic and pervasive iodine deficiency within much of our population.

    I wonder whether any of the learned contributors to TC can help me with a question that's been exercising my mind of late in that regard, which is to do with a clear discrepancy in academic achievement between Asian students and the rest? Could that discrepancy have any relationship to diet, particularly the consumption of marine foodstuffs high in iodine?

    Typically cultural factors are cited, but I've not seen any real evidence of causation in what I've read on that topic, so is there a physical factor?

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    1. Daniel Boon

      logged in via LinkedIn

      In reply to Craig Minns

      Craig .... I like your response (I say this having been to several other forums where individuals have a barrow to push and little else) ... and I agree with there being many factors and I will include a anecdotal incidences .... the 'tall poppy syndrome' is prevalent throughout all societies, seen as a threat, so some people dumb themselves down to be seen as less of a threat ... boys (Jackass) do some dumb-arse things, they over-do and just as some people are more quickly affected by alcohol, so too is it with any drugs ...

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    2. Craig Minns

      Self-employed

      In reply to Daniel Boon

      Thanks Daniel.

      I'm sure those factors you cited are important, but surely a lack of iodine is easily fixed by supplementation in foods? We did it for folate with ease and a good job too.

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    3. Daniel Boon

      logged in via LinkedIn

      In reply to Craig Minns

      You're right Craig ...

      But when you come down to it ... hasn't increasing the human population with a decreasing IQ proved flawed enough already, you cannot educate everybody ... the Planet has a maximum carrying capacity and survival of the fittest is supposed to be the leveller ... you ever checked out the Darwin Awards ?

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    4. Dennis Alexander

      logged in via LinkedIn

      In reply to Craig Minns

      Hi Craig,
      Very good point. It (iodine deficiency) used to be known as "cretinism" due to its prevalence on Crete. In Tasmania in the 1960s there was a regular supplementation program in schools - goiter pills.

      On the Asian front, you might first want to have a look at Outliers by Malcolm Gladwell which does have aplausible explanation on the Maths front. I'm not sure that there is a benefit effect from increased iodine above the acceptable range - it is a poison in quite small daily doses. Sea salt and iodized salts are often recommended to avoid hypothyroidism.

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    5. Craig Minns

      Self-employed

      In reply to Dennis Alexander

      I used to see lots of goiters growing up in PNG. Highlanders were very prone to it and sea salt was a highly prized trade good.

      From all I read, the mean Australian diet is deficient and becoming more so, thanks to increased use of pre-processed food and hence less addition of iodised salt at home, while the manufacturer uses plain NaCl. My speculation was whether the typical Asian diet as seen here, with lots of seafood, might be actually within the acceptable range, meaning that the mean for the rest is even worse.

      Thanks for the reference, I think I've seen it mentioned before. I'll have to look it up.

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    6. Daniel Boon

      logged in via LinkedIn

      In reply to Craig Minns

      Its a commercial - profit driven - decision to remove iodine from salt ... iodised salt is usually sparse on grocery shelves if at all ...

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    7. Craig Minns

      Self-employed

      In reply to Daniel Boon

      I've had no trouble, I always use it.

      Dennis's point about overdose is very good. Perhaps it could be added on a semi-random basis to batches of food, so that the net intake is about right or a little below and nobody's likely to get an excessive dose on an on-going basis? A slightly higher intake might also get people's metabolisms moving and hence reduce obesity.

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    8. Sue Ieraci

      Public hospital clinician

      In reply to Craig Minns

      Although Australia hasn't seen severe, or congenital, iodine deficiency for some time, there is some evidence that mild deficiency is re-emerging in older children. A recent study in western Sydney found approx 50% of urinary levels below the recommended level, but only in children older than 2 years. This was a test-based study, though, not correlated with any real outcomes.

      A 2010 MJA opinion piece discussed re-emerging mild iodine deficiency in pregnant women:
      https://www.mja.com.au/journal/2010/192/8/iodine-deficiency-australia-iodine-supplementation-pregnant-and-lactating-women

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    9. Carol-Anne Croker

      logged in via Facebook

      In reply to Dennis Alexander

      I went through a sustained period of iodine treatment before thyroid surgery and knew that our local area is deemed an area of concern for lack of iodine in diets. This may be because I live in a lower SES area and our seafood/ shellfish consumption is also comparatively low.

      No one issue comes down to one fix all solution. Iodine dietary supplements, great in principle but what of human choice and agency?

      In Australia we have noticed that the word goitre does not occur as often as it once…

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    10. Carol-Anne Croker

      logged in via Facebook

      In reply to Daniel Boon

      In the catering Industry (according to my son) they always seek 'natural' i.e. iodised salt in cooking.

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    11. Carol-Anne Croker

      logged in via Facebook

      In reply to Sue Ieraci

      Thank you for bringing in the geographical aspects to this discussion it gives credence to what I hear in various conversations in my workplace/s.

      Interesting again the study was conducted in Western Sydney. Geography or SES? How to discount one factor from another?

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    12. Craig Minns

      Self-employed

      In reply to Sue Ieraci

      Hi Sue,
      thanks for that MJA piece, I hadn't seen it before.

      Your point about diet is a good one, perhaps I should have been more specific about geographic origin. However, I think my original point stands in general for Australia, at least up until recent times when we have had an influx of ethnic Tamil and other groups from South Asia who may come from more inland areas or have a vegetarian lifestyle that doesn't include seafood. Most of our Asian population previously was from SE Asian or coastal…

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    13. Martin Male

      logged in via Facebook

      In reply to Craig Minns

      Hi I would also like to comment on the openness in this discussion. It is great to have discussion without personal vilification ;)
      Just a little correction about vegetarian diets"vegetarian lifestyle that doesn't include seafood". I have been vegetarian since '81 and eat seaweed products and salt from the himalayas. It may not be accurate to assume that vegetarian diets lack iodine? Most vegetarian diets include seaweed products.I know that tofu is made with seaweed product.

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    14. Sue Ieraci

      Public hospital clinician

      In reply to Craig Minns

      Hi, Craig

      Ultimately, there will always be difficulty sorting out the various contributors to high academic achievement - from native intellect or "IQ" to motivation, pressure, culture, conformity, sheer hard work, time spent studying, exam technique etc etc

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    15. William Hughes-Games

      Garden weed puller

      In reply to Craig Minns

      Asian students study hard. In so far as smoking pot takes up the time and reduces the incentive to study, pot smokers fall behind. How much more mellow to light up, chill out rather than trying to work through some complex maths problem. It has been shown pretty conclusively that the brain develops with use all our life in contrast to what was once believed. Any crutch, alcohol included, will reduce the real 'exercise' that your brain gets. The teen years from about 12 to 25 are a period where the brain is particularly able to develop and yet this is exactly the period when silly teens start to use tobacco, pot and alcohol. What a waste. No wonder they call someone high on pot "wasted".

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  2. Michael Shand
    Michael Shand is a Friend of The Conversation.

    Software Tester

    Interesting, nothing suprising, Just out of curiosity, I mean the evil marijuana plant lowers your IQ if you start taking during your teens.........how much more evil is marijuana compared to alcohol?

    IE. marijuana drops your IQ - fine, completely sane and understandable statement but can you put this in context? how much does alcohol abuse lower your IQ? how much does ecstacy? how much does ADD medication?

    I dont see that this peice gave any useful or new information other than "This particular Drug is Bad hmmmmkay" - yeah we get it, its not exactly a slice of avocado but neither is ethanol or tabaco or speed or caffeine

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    1. Carol-Anne Croker

      logged in via Facebook

      In reply to Michael Shand

      More research on effect of all stimulant and depressant products on our neurobiology. Very valid point, but one 'drug' needs study over time before the testing can be replicated across a range of abused sustances. I am sure this is occurring in other Centres for Research around Australia, but the contributors here can only speak from their own research and analysis, rather than generalise and make unfounded/untested hypotheses.

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  3. William Bruce

    Artist

    I can attest I know many, many people who have gone "Veg" smoking too much reefer...
    ... lives have often messed up..
    . We need to educate ALL 12 year olds (with video presentations from SCIENTIST & Ex-users) ...and let kids ALL know that when you get older you can take all sorts of drugs but it will certainly give you BRAIN DAMAGE... AND can very seriously harm your health & shorten your life!!
    Educate & LEGALISE....stop the corruption of EVERY organ of our society...drugs are a health issue not a crime AND they are a HUGE drain on the public purse.

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    1. Michael Shand
      Michael Shand is a Friend of The Conversation.

      Software Tester

      In reply to William Bruce

      I'm still interested to hear about the affects of alcohol consumption, it kills far more people every year than weed, can have the same effect on your brain as weed but we dont get massive articles about the dangers of drinking - what we get is this selective BS from people pushing an agenda, I agree with you that we should legalise

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    2. Tim Benham

      Student of Statistics

      In reply to Michael Shand

      I see anti-alcohol ads on TV regularly, certainly more frequently than I see anti-cannabis ads. Several posters seem keen to change the subject (to alcohol or iodine). Are they defensive of the drug they consume?

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    3. Craig Minns

      Self-employed

      In reply to Tim Benham

      I guess you must have been in a hurry and simply didn't have the time for reading the whole of my posts, Tim. I'm sure you've done so by now.

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    4. William Bruce

      Artist

      In reply to Michael Shand

      I agree .
      Sorry, I intended that alcohol be included in the "drug" catagory...

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    5. In reply to Tim Benham

      Comment removed by moderator.

    6. Michael Shand
      Michael Shand is a Friend of The Conversation.

      Software Tester

      In reply to Tim Benham

      Thats interesting, you may notice that neither my comments nor the others were trying to change the subject but merely asking for context.

      ie. Drug A causes your IQ to be lowered by 10 points - goshhhh.....is that a lot? is that more than other drugs? or is that expected over time?

      Its not a change in subject, its asking for detail on the current subject.

      You say you see Anti-Alcohol ads all the time....I have seen ads desecriminating against drinking habits in front of your children, I have seen ads about drinking and driving, I have seen ads about drinking responsibly.....I havent seen any ad that is against drinking all together - have you? ie. Alcohol is a toxin, it enters your body and destroys your brain cells, every drink you take is making you dumber.....havent seen that yet, if oyu have thats awesome, cna you please link in response

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    7. Sean Manning

      Physicist

      In reply to Tim Benham

      They are not anti-alcohol ads but drink responsibly ads. There is a key difference there. We are being told to not go near drugs because they will ruin you but alcohol is ok, just don't be silly with it.

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    8. Carol-Anne Croker

      logged in via Facebook

      In reply to William Bruce

      Warning young people even via the best intentioned education programs won't work, nor does compulsory legislation to ban substances of harm.

      We were all young and felt bulletproof once. The "it won't happen to me attitude" lives a long time in our Culture. Think of road trauma.

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    9. Carol-Anne Croker

      logged in via Facebook

      In reply to Tim Benham

      Doubt it is defensiveness. Think it is just that once an article is posted the discussion can go in any direction. I see so many issues linked across sociological, psychological, medical and other disciplinary silos that often the thinkers/commentators do not get a chance to reflect across disciplinary lines very often, nor are we in our Universities to research so collaboratively unfortunately.

      Where some see "barrow pushing" or "agendas" I see an need for more constructive sharing of perspectives, without resort to negative postings in response to disagreements.

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    10. Carol-Anne Croker

      logged in via Facebook

      In reply to Pauline Zardo

      But again a different research topic for discussion not related to the questions posed for further research in this one specific area. Acohol abuse and treatment initiatives are active sites for research globally also.

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    11. Sue Ieraci

      Public hospital clinician

      In reply to Tim Benham

      Tim Benham is right - the effects of excessive alcohol on the brain are well-known and often publicised.

      This is an article about cannabis. There seems little point in criticising the author for not mentioning everything else besides cannabis.

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    12. Sue Ieraci

      Public hospital clinician

      In reply to Michael Shand

      "Alcohol is a toxin, it enters your body and destroys your brain cells, every drink you take is making you dumber.....havent seen that yet"

      That's because it isn't true, Michael Shand. Alcohol is not a toxin in small amounts, and every drink does not destroy brain cells.

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    13. Tim Benham

      Student of Statistics

      In reply to Michael Shand

      @PZ alcohol may cause larger "societal problems" but so what? The study was about cannabis, not alcohol.

      @MS a comparative study of the effects on IQ of cannabis and various other drugs would be an interesting thing, but it is still worth considering this study first. What is an "anti-alcohol" ad is perhaps subjective. The ads seem to me to convey that alcohol can make you stupid and violent, lead to social humiliation and rape, and make you throw up. I wouldn't call it a positive message.

      I can't remember seeing any anti-cannabis ads on TV. I've seen a few low key ones on bus shelters advertising treatment services for people who think they have a problem. Searching youtube found one from 2007. http://www.youtube.com/watch?v=DC0O5OVnDkY

      I don't think that it is true that every drink destroys brain cells. That has the aroma of an urban myth. Do you have any reliable references?

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  4. Comment removed by moderator.

  5. alexander j watt

    logged in via Twitter

    Rogeberg states in his conclusion that "heavy, persistent, adolescent- onset cannabis use involves a culture and norms that raise the risk of dropping out of school, getting entangled with crime, and other such behaviors. Unlike a neurotoxic effect, however, this effect would be nonpermanent and mediated by the cognitive demands of different environments. Because the effect in this case would be a result of culture rather than pharmacology, it would also have different policy implications."

    I…

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  6. Colin MacGillivray

    Architect, retired, Sarawak

    Good article. I'm sure these questions have been answered elsewhere.
    The Dunedin longitudinal study was of about 1000 babies born in 1972-3.
    How many were regular adolescent cannabis users?
    Was the Flynn effect taken into account?

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    1. Carol-Anne Croker

      logged in via Facebook

      In reply to Colin MacGillivray

      Will be looking up the Fynn effect. Would like to know more, the age of it (when written) and any additional validation. Thanks for more additions to my knowledge stores... as an writer and sessional academic I find many uses for 'research' :-)

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    2. Craig Minns

      Self-employed

      In reply to Colin MacGillivray

      The Rogeberg analysis of this data.

      http://www.pnas.org/content/early/2013/01/09/1215678110.short

      "The association is given a causal interpretation by the authors, but existing research suggests an alternative confounding model based on time-varying effects of socioeconomic status on IQ. A simulation of the confounding model reproduces the reported associations from the Dunedin cohort, suggesting that the causal effects estimated in Meier et al. are likely to be overestimates, and that the true effect could be zero. Further analyses of the Dunedin cohort are proposed to distinguish between the competing interpretations. Although it would be too strong to say that the results have been discredited, the methodology is flawed and the causal inference drawn from the results premature. "

      Here's some supporting detail from Reogeberg

      http://www.pnas.org/content/suppl/2013/01/09/1215678110.DCSupplemental/pnas.201215678SI.pdf

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    3. Craig Minns

      Self-employed

      In reply to Colin MacGillivray

      Hi Colin,
      Thanks for the Flynn effect info. I'd heard of it, but wasn't aware it had been so well-explored.

      The nutritional hypothesis to explain it would encompass things like iodine deficiency, which historically has been a much more serious problem than it is today, even though there seems to be something of a regression in that regard within Australia. Some areas (Crete was mentioned by an earlier poster and other areas with little access to sea salt are the same) have had endemic iodine deficiency for centuries, which the revolution in transport through the 19th and 20th centuries helped address.

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  7. William Hughes-Games

    Garden weed puller

    It might be that smoking Pot doesn't actually damage the brain of a teen but I can tell you as a former Math Teacher that a zonked student is completely incapable of absorbing anything taught in class. People have two periods of amazing learning ability. The greatest is from age 0 to about 7 years and the second during the teen years. Smoking pot is like dragging the edge of a fine blade across a rock. It can no longer cut it.

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  8. Martin Male

    logged in via Facebook

    Hi Whilst I see merit in this study I challenge the attention to dope smoking. I used to be a heavy user in my youth (sound like an old man:) ) I am now a psychotherapist and don't smoke. I have no doubt that there are effects, yet I would also question whether this is a result of the modern hydroponic methods and the chemical residue that is in the plants. It would be interesting to have a study that has people from India and Jamaica, as there is a long culture practice of smoking and there supplies…

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    1. Russell T

      IT Consultant

      In reply to Martin Male

      I also smoked a lot of dope when I was in my teens. That was before hydroponic crops. I am pretty sure it had a dramatic affect on my development, emotionally and academically I was affected. However I stopped when I reached my early twenties. The problem is I also drank heavily and enjoyed taking speed in this period so figuring out what effect was caused by what is problematic.
      The point I would make is that in my case the affect was temporary, or at least I would like to think so. I now don't smoke, drink alcohol, or participate in recreational drugs use and haven't since becoming a parent.
      So if there is an effect - is it temporary? And I also find it difficult to think of many dope smokers who didn't drink alcohol (in what is now viewed excessive amounts) or use other recreational drugs which makes me wonder if it is really possible to discern the real effects of dope smoking on youth.

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    2. Tim Benham

      Student of Statistics

      In reply to Martin Male

      The idea that modern dope is somehow completely different and much worse because it is grown hydroponically is just drug war propaganda. I have grown in soil and in rockwool and it made no difference to the effects of the product. Why would it? hydroponics is just the use of an artificial growing medium instead of soil.

      Growing indoors has three benefits. The plants grow faster because the artificial sun never has to set. You can control when flowering occurs. And no-one can see your plants.

      The idea that "hydroponic dope" is unnaturally potent persists because it suits both WoD warriors and drug dealers. The THC concentration has increased over the decades due to selective breeding. It may have increased by a factor of perhaps four since the 1970s, but strong Thai "buddha sticks" then were as strong as anything today.

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    3. Martin Male

      logged in via Facebook

      In reply to Tim Benham

      Hi Tim thanks for your perspective. My view was more about the chemical residue from the products from the hydroponic system. There are no chemical residue from cannabis grown in the soil as none are added, a least when I used to grow it, apart from cow and chicken manure?

      I would be interesting to see if there is any research on either chemical residue in the dope from hydroponic system . Also it would be interesting to see of THC content has changed.

      By the way I am neither a dope dealer or a WOD warrior ;) I consider that people have the choice of what they put into their body, along with the consequences of all their choices.

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    4. Tim Benham

      Student of Statistics

      In reply to Martin Male

      "Chemicals" aren't the spawn of the devil. People are made of chemicals. The chemicals necessary to hydroponic growing are the nitrates and other salts containing the nutrients (N, P, K etc) a plant needs. They are otherwise known as soluble fertilizers.

      Some growers add funny stuff that is supposed to make the buds bigger or whatever. I think they're mugs. Phostrogen works fine.

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  9. Martin Male

    logged in via Facebook

    Has anyone seen the doco Breaking the Taboo. I agree with Carol-Anne and Russell's comments. If as a society, we really do want to address the "issue of problem drugs" , we must include all drugs including alcohol and prescription drugs, then we need a multi-factorial and multidisciplinary approach. Both my personal and professional experience, including working working in a juvenile detention centre and a detox unit, has shown me that rarely does a person use just one drug, for one reason. Humans…

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    1. Russell T

      IT Consultant

      In reply to Martin Male

      Martin,

      I don't don't know about others; however my drug experience including alcohol was totally about fun at first. It was a mix of heightened states and youthful exuberance brought on, I imagine by the rebelliousness of what we were doing. It was all mixed up with music, surf, drama, and being out there. Don't imagine that this is about blocking anything out. At the time it was totally about having fun, then steadily it changed to not being fun. I keep reading about people taking drugs to block…

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    2. Russell T

      IT Consultant

      In reply to Russell T

      PS I meant to say I didn't expect total abstinence as believe is not a reasonable or achievable.

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    3. Nick Stafford

      writer

      In reply to Russell T

      Hi people

      it is great to read people just talking honestly about their drug experiences. I too have used most of the illegal drugs, and enjoyed myself immensely, and suffered from addiction.

      The biggest problem we face is that:

      Most alcohol users, and us as a society, are in denial of our drug use.

      With the currently illegal drugs we only ever discuss the negative side.

      The truth with all our drugs, legal, illegal and prescription, is that nearly all people are using them for a mixture…

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    4. Martin Male

      logged in via Facebook

      In reply to Russell T

      Thanks for taking the time to write such a thoughtful and insightful response. I see that most of us start taking drugs to avoid the feeling of emptiness or disconnection from our deeper self that our society has encouraged. In more traditional societies this is done with drug/mind altering practices.
      In your response you touch on this "a strong community with all ages involvement that gets children and teenagers continually involved in positive life experiences will reduce the odds of teenagers…

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  10. Matthew Albrecht

    Postdoctoral Researcher at Curtin University

    Another way to look at this research is that you have to be a massive stoner for almost a couple of decades to have any kind of deleterious effect of cannabis consumption on cognitive performance (which is on average a 6 point drop for the most dependent users as per the paper). And only but the most severe users will manifest such a drop. One then wonders about many of the points brought up in the comments about co-morbidity, other drug use etc. I suppose people shouldn't be too surprised that sitting on the couch, eating doritos and playing video games doesn't do wonders for your cognitive capacity? :)

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    1. Martin Male

      logged in via Facebook

      In reply to Matthew Albrecht

      I didn't eat doritos in my day, we did have footlong hot dogs though. That was really greening out !!
      We did sit on the couch talking lots about ways to change the world and what was wrong with it, whilst watching Cheech and Chong;). We also consumed lots of tequila and beer.

      I must agree that it does now seem obvious that this "doesn't do wonders for your cognitive capacity". It reminds me of the line from Cocaine by Jackson Brown "I gotta take more of it or less of it....(reply of friend) It takes a clear mind....It takes a clear mind to take or not to take it.......(reply of friend) It take a clear mind to make it. ;)

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  11. Russell T

    IT Consultant

    What I would like to see is research on the adult community to see whether at age, say 40 is there evidence of a continuing impact on ex users who haven't touched cannabis for 10 years. The reality is most people do grow up and stop using recreational drugs. It is part and parcel of maturing into a responsible adult who has responsibilities and accepts that they can't do both (at least most of us stop).

    So is there a real deficit for those who did participate for 1, 2, 5, 10, 15 years? And how does that deficit manifest itself? The research probably exists; but I haven't seen it. Can anyone point me to it?

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    1. Nick Stafford

      writer

      In reply to Russell T

      Dear Russell

      it is completely untrue to say that "most people do grow up and stop using recreational drugs."

      Most from my experience simply cut down on the range of drugs they use as they move into their 30s, but they never stop. Alcohol and caffeine are used by many older Australians.

      Your notion that "growing up" involves, or should involve stopping drug use is moralistic nonsense.

      grown up adults around the globe have been using drugs for centuries and will always do so. It is just…

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    2. Russell T

      IT Consultant

      In reply to Nick Stafford

      I apologise, I should clarify :) Most people stop using illegal drugs by the time they reach their 30s. And lets drop the label growing up and add make it - they adopt more socially acceptable stance, in Australia that generally means use of alcohol as a substitute.

      Sorry I don't see caffeine in the same vein as Cannabis, Alcohol, Acid etc.

      And yes socially drugs are often (not always) parts of many societies.

      However I would still like to see if there are provable long term cognitive consequences for those who have stopped using cannabis. I personally can't see it in those I know who used to smoke cannabis with me, to all appearances seem to have actually adapted to middle age and work life with less problems than many around them. However that involves a very small snowball sample ;)

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    3. Nick Stafford

      writer

      In reply to Russell T

      Hi Rusell

      I take your point that you meant people stop using illegal drugs, and your valid view about what you meant by "growing up".

      I know many people in their 30s, 40s, and 50s who used to use a lot of drugs in their 20s, and some who still use a lot of drugs.

      While my sample size is small as well, I have worked in the drug user movement nationally and internationally for 20 years so my sample size is considerably larger than most peoples.

      It is clear to me that how well these people…

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    4. Martin Male

      logged in via Facebook

      In reply to Nick Stafford

      Hi again I thank everyone for their insightful and open perspectives
      Nick I would agree with what you have written is posted in my last effort . Mind altering experiences are essential to open our self the true nature of the amazing planet we live on and the interconnectedness on us all;)

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  12. Danny Hoardern

    Analyst Programmer

    Thanks, an interesting article and a good find by Rogeberg; SES is an important factor when researching IQ - you would think Meier's original study would have picked this up when determining which factors play a role in adolescent IQ differences. Perhaps for simplicity they had to draw the line somewhere.

    Cannabis allows you to access more of your memories[1-2] which is linked to creativity - what sane adult, given the choice, would say no if they were offered access to more of their memories…

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  13. Yoron Hamber

    Thinking

    Sorry but this reminds me of that dutch study in where the dutch police wanted to prove how dangerous hashish was, quite some time ago. They locked one volunteer policeman in a cell as he smoked as **'. And sure enough, he ended up pooing himself, getting all kinds of disturbing effects :)

    Intelligence is not a God given scientific definition of anything in fact, it's a subjective definition differing from country to country although researchers try to get to a common basis. Einstein wasn't the brightest light in his class for example, although he, as we now know, was a genius by all standards.

    This kind of study is made to be questioned I'm afraid, on so many points. It has so much to with what a person expect himself capable of etc.

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  14. Matt Stevens

    Senior Research Fellow/Statistician/PhD

    I think the main issue with the study (though I haven't seen the whole statistical analysis - only had access to the abstract) is the problem of confounders (unmeasured variables). As a number of the comments attest, nearly all drug (including alcohol) users, use multiple drugs. Unless some of these interactions are tested in statistical models, then it means nothing. I am not sure if they controlled for further education or just baseline education, whether parental education, employment change etc…

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    1. Martin Male

      logged in via Facebook

      In reply to Matt Stevens

      Hi Matt I agree with all you have said. It would be interesting to do a cost benefit analysis on the costs of "the war on drugs" specifically in relationship to cannabis ;)

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  15. Yoron Hamber

    Thinking

    IQ is as much a expression of what a society finds useful as a 'objective' science to me. Why would the tests change if it was 'objective' :). You can always argue that it is more of a science today of course, than yesterday, but nah, we still have some way to go to that, as I think.

    Also, as someone pointed out, your environment will define that 'IQ', and the way your interests goes, as in reading books for example, or not.

    On the whole a subjective definition I think, although marijuana is a drug, not any 'thought enhancer' :) But we humans have used it for a very long time , haven't we? As recreation and as a way to communicate with each other. Same as booze as far as I'm concerned, with similar problems for those using it daily. It's primary a social question if it used or not, instead of drinking.

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  16. William Hughes-Games

    Garden weed puller

    I have no idea if pot physically lowers IQ or not but what is sure, it lowers the users sharpness and interest in class during the second most important period in the person's life in terms of brain development (the first is from 0 to 5 years). A person who is off his face or even hung over in class learns nothing and hence falls behind his peers.

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  17. John Hopkins

    Social Engineer

    Cannabis DOES NOT cause lowered IQ. I have been smoking daily for over 30 years. IQ 145 30 years ago & IQ 135 now. I started at 15. Every adult I know smokes Cannabis. Most of them daily. No "lowered IQ" as per these rediculous claims. This "Study", is YET ANOTHER government sponsered "fixed study" to backup stupid governments continuation of "Marijuana Madness.
    People are simply not dumb enough to buy it any more.

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    1. Ben Rich

      PhD at Monash University

      In reply to John Hopkins

      "Cannabis DOES NOT cause lowered IQ I have been smoking daily for over 30 years. IQ 145 30 years ago & IQ 135 now"

      One of these statements doesn't support the other.

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    1. John Hopkins

      Social Engineer

      In reply to William Hughes-Games

      Even my hero, Stephen Hawking, makes the occassional typo. Your response is very typical of those brainless dimwits who say that Cannabis lowers IQ.
      You'd have to get a group of them to have one brain between them.
      And, Mr Dopey, my "trade" is as an IT professional. Strictly the domain of the higher IQ's within our communities.
      Now I am doing a degree in Science. My memory is UNCANNY. I can remember even the smallest details.
      So, "lowering IQ" & "Memory deficiencies" are YET ANOTHER relic of our rediculous "Marijuana Madness". Though I prefer to call this Phenomenon "Lack Of knowledge about Cannabis, STUPIDITY"

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