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Use of Cannabis at Young Age Lowers Intelligence

Use of Cannabis at Young Age Lowers Intelligence

cannabis, smoking, research, Proceedings of the National Academy of Sciences, IQ, intelligence, teenagers
Smoking cannabis may be especially harmful among teenagers who are under 18 years of age, but it may be relatively safe for ‘over-18 brains’, according to new research published in the Proceedings of the National Academy of Sciences.

The paper is based on a follow-up of more than 1,000 individuals since their birth to age 38. They were interviewed at certain ages to learn about their substance abuse habits, among other aspects, and two neuropsychological tests were conducted at ages 13 and 38.

The results showed that people that started smoking at an early age experienced a higher neuropsychological decline, with an IQ drop of 8 points on average. Also, giving up the habit at some point of their adult life didn’t seem to bring a significant improvement.

‘Collectively, these findings are consistent with speculation that cannabis use in adolescence, when the brain is undergoing critical development, may have neurotoxic effects,’ write the researchers.

‘This work took an amazing scientific effort,’ adds Prof Terrie Moffitt of King’s College London’s Institute of Psychiatry, and co-author of the study. ‘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.’

Source: BBC News, The Guardian

Photo: Wikimedia Commons

Madeline H. Meier, Avshalom Caspi, Antony Ambler, HonaLee Harrington, Renate Houts, Richard S. E. Keefe, Kay McDonald, Aimee Ward, Richie Poulton, & Terrie E. Moffitt (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1206820109

Recommended Reading:

Effects of cannabis
Publisher: Alphascript Publishing

Jaime Menchén
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12 Comments

  • Clarisse
    August 28, 2012, 17:58

    I don’t completely agree with this studies results. Based on my past experiences and what I’ve seen in fellow peers, it really does effect you’re thinking levels not necessarily you’re intelligence! I myself since using cannabis have lost my ability to focus as well as my memory is pretty shot; but I still do just as great in school as I did before I smoked. It’s more challenging due to the effects but I’m just as intelligent as I once was. An A and B student!

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  • Clarisse
    August 28, 2012, 18:46

    I don’t completely agree with this article. I believe that the use of cannabis at a young age can affect the functions of the brain.. not necessarily the intelligence. As a previous cannabis user I feel that I’ve developed significant memory loss as well as focus issues. Mind you I am a 18 year old female. I started smoking around age 14. These factors may in turn effect someone’s intelligence academically but not straight towards their intelligence. I still manage good grades (As and Bs) it’s just a bit harder now. There is defiantly a positive correlation of the two but there are other factors besides just cannabis use.

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    • Jaime Menchén@Clarisse
      August 29, 2012, 11:55

      Well, the problem may be with the definition of intelligence in itself. What the authors of the paper say is that it affects the IQ, which is just one way to measure intelligence. When you admit having developed memory loss and focus issues, that’s related to intelligence as well, at least according to the IQ. The main point of the paper is that cannabis consumption at an early age is actually harmful, and its authors explain in what ways it may be so. You have to keep in mind, however, that cannabis may affect people in different ways, and I agree that there are many factors involved regarding academic performance and personal development, as the authors of the paper do; in fact, they checked all abuse substance consumption among the participants, as well as other circumstances, before drawing any conclusions. Anyway, the results of the paper don’t mean that a person who consumed cannabis at an early age may become a bad student but, as you also recognize, that it may become harder for her/him to keep up the good grades.

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  • Brendan Kennedy
    August 29, 2012, 05:48

    Marijuana users are more likely to order Chinese food and watch star trek rather than go to class, which could result in a lower I.Q. (biased on just lack of motivation) lol. However i do agree that extensive abuse of drugs and alcohol can cause negative effects on a young developing brain. I wonder how many uses of the cheebah it takes to have a negative effect on the young brain. interestingly enough, I’m sure the negative effects (both mentally and physically) of marijuana(illegal) are less detrimental when compared to the negative effects of alcohol(legal).

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    • Jaime Menchén@Brendan Kennedy
      August 29, 2012, 12:16

      The thing is that the harmful effects of alcohol on the young brain are well known, while, believe it or not, there was no comprehensive research on the effects of marijuana consumption on teenagers. One of the triggers of this study was the fact that more and more teenagers were starting to consume cannabis without being aware of its long-term harmful effects. The results of the study seem quite conclusive, though there are many other factors, of course, involved in the teenager’s development.

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  • Tyler C
    August 30, 2012, 03:28

    I believe that yes, cannabis has a positive correlation on the brain. But their are many factors that can contribute to IQ level. I don’t believe that someone that smokes say once a week will be affected by it as much as someone who smokes 5g daily. I have many friends that go out and party all the time and still are able to retain a very high GPA. IQ is just one way to measure intelligence, its not completely universal. For instance David Wechsler (designer of the intelligence test called the WAIS) believed intelligence was involved a number of mental abilities. Yes he used IQ scores but he believed that the scores could be affected by personality, cultural factors, and motivation.

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    • Jaime Menchén@Tyler C
      August 30, 2012, 12:46

      I agree with the statement that IQ is just one way to measure intelligence. Also, it is not the same to smoke once a week than smoking 5g daily, as you say, and I believe the authors of the paper take this into account. What defines intelligence is still up for debate; maybe it would be a good topic for another article.

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