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Study: Marijuana Use Not Predictive Of Lower IQ, Poorer Educational Performance


colorado schools marijuanaBy Paul Armentano, NORML Deputy Director

Marijuana use by adolescents is not associated with lower IQ or poorer educational performance once adjustments are made for potential confounders, specifically cigarette smoking, according to longitudinal data published online ahead of print in the Journal of Psychopharmacology.

British investigators assessed the relationship between cumulative cannabis use and IQ at the age of 15 and educational performance at the age of 16 in a cohort of 2,235 adolescents.

After researchers adjusted for potentially confounding variables, such as childhood depression and cigarette use, they reported, “[T]hose who had used cannabis [greater than or equal to]50 times did not differ from never-users on either IQ or educational performance.”

By contrast, teen cigarette smoking was associated with poorer educational outcomes even after researchers adjusted for other confounding variables.

Researchers concluded, “In summary, the notion that cannabis use itself is causally related to lower IQ and poorer educational performance was not supported in this large teenage sample.”

A widely publicized New Zealand study published in 2012 in The Proceedings of the National Academy of Sciences reported that frequent use of cannabis by those under the age of 18 was associated with lower IQ by age 38. However, a separate review of the data published later in the same journal suggested that the changes were likely the result of socioeconomic differences, not cannabis use.

More recently, the results of a 2015 study in the journal Drug and Alcohol Dependence reported that the effects of persistent adolescent cannabis use on academic performance “became non-significant after controlling for persistent alcohol and tobacco use.”

Full text of the study, “Are IQ and educational outcomes in teenagers related to their cannabis use? A prospective cohort study,” appears online here.

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Johnny Green


  1. If heavy Marijuana use led to lower IQ, Berkeley, Stanford, MIT and Harvard would be in real trouble. :-)

  2. Yes, the Bablyon system is about power over others for domination and exploitation. There is another way, in fact, in the long run it is the only way that life can be sustained, thrive and reach its full potential. It is the way of non-power and empathy.

    A wounded, broken and dying world cannot find its way to an all-powerful god above and beyond. What the real world needs is a god (a servant god, not a proper god at all) that comes to it and unconditionally gives it, all of it, liberation from oppression and fear and healing for those who have been grievously harmed and damaged by the death-dealing powers of this world.

    Where do you find evidence of such a god? In many things; small and unpretentious things like the microorganisms (bacteria, fungi) and plants especially the cannabis plant, which are foundational for all life on the planet.

    Cannabis, a not particularly glamorous looking plant, often called a weed, it is a true miracle of nature. Miracle not in the commonly understood sense of an extraordinary supernatural event, but in the sense of the original Latin miraculum – a wonder. It gives freely (only Babylonian prohibition forces most to pay dearly for it) to those who partake of it: It meets our most essential needs: The liberation of the mind from fear and painful memories; it opens up our minds to the larger universal consciousness and makes us more empathetic. Its seeds and leaves are among the most nutritious of foods. It does not “cure” like pharmaceuticals, it instead enables the body to heal itself without harming the overall health of the person with harsh side effects.

    It is as true wonder of nature and a wondrous harbinger of what is coming towards us from beyond the far horizon.


  3. Babylon system has to fall. It’s corner stone is lies slavery and oppression
    love is the answer the only path to god

  4. Fungi Sclerotia 1427 on

    What do those Rethug prohibitionist hypochristians know about “Jesus”?

    Heard that He was anointed with a healing mixture that included
    Kaneh Bosm / cannabis, (incorrectly-translated as “calamus”).

    We need to throw the “Good Book” at them!!!
    [correctly-translated, of course].

  5. They said they love to workout or swim after getting high. It makes swim really great. They feel great and vaporize daily.

  6. Such a society will inevitably self-destruct. The real tragedy is that it will take a lot of innocents down with it.

  7. However, cannabis users can benefit from a higher EQ (empathy quotient) which helps them to be more empathetic to the feelings and perspectives of others (and not just the human others) and to new ways of seeing the world that is less phobic and more inclusive. A higher EQ in the long run trumps a high IQ. Someone who has a high IQ with a very low or non existent EQ is a high functioning psychopath — extremely dangerous. High IQ without a robust EQ leads to crises like the sixth and fastest mass extinction event that we are currently in the midst of.

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