Yet Another Study Finds That Cannabis Use Is Not Independently Linked With IQ Decline

  • by Paul Armentano, NORML Deputy Director August 3, 2017

    Marijuana researchCannabis use by teens is not independently linked with adverse changes in intelligence quotient or executive functioning, according to longitudinal data published online ahead of print in the journal Addiction.

    A team of investigators from the United States and the United Kingdom evaluated whether marijuana use is directly associated with changes over time in neuropsychological performance in a nationally representative cohort of adolescent twins. Authors reported that “family background factors,” but not the use of cannabis negatively impacted adolescents’ cognitive performance.

    They wrote: “[W]e found that youth who used cannabis … had lower IQ at age 18, but there was little evidence that cannabis use was associated with IQ decline from age 12 to 18. Moreover, although cannabis use was associated with lower IQ and poorer executive functions at age 18, these associations were generally not apparent within pairs of twins from the same family, suggesting that family background factors explain why adolescents who use cannabis perform worse on IQ and executive function tests.”

    Investigators concluded, “Short-term cannabis use in adolescence does not appear to cause IQ decline or impair executive functions, even when cannabis use reaches the level of dependence.”

    Their findings are consistent with those of several other studies – including those here, here, here, and here – finding that cannabis use alone during adolescence does not appear to have a significant, direct adverse effect on intelligence quotient.

    widely publicized and still often cited New Zealand study published in 2012 in The Proceedings of the National Academy of Sciences reported that the persistent use of cannabis from adolescence to adulthood was associated with slightly lower IQ by age 38. However, a follow up review of the data published later in the same journal suggested that the observed changes were likely due to socioeconomic differences, not the subjects’ use of cannabis. A later study by the initial paper’s lead investigator further reported that the effects of persistent adolescent cannabis use on academic performance are “non-significant after controlling for persistent alcohol and tobacco use.”

    16 responses to “Yet Another Study Finds That Cannabis Use Is Not Independently Linked With IQ Decline”

    1. TheOracle says:

      This study, along with Mitch Earleywine’s sinking of the validity of the marijuana gateway theory, needs to be trumpeted and drummed into people via TV potumentaries like those that Trish Regan, Harry Smith, and Dr. Sanjay Gupta have done. There were other shows: Weed Wars, Weediquette, etc. Thing about Weediquette is that it’s on VICE, and VICE is not a premium cable channel in my neck of the woods, whereas before it came with the Comcast add-on package. I guess rather than use their V-chip and parental filters on Comcast they just bitched or something.

      Thank you for making Amsterdam in the desert a reality. Nipton, California, I sort of thought Amsterdam in the desert would be on the Nevada side of the border, but hey, it’s The Amsterdam of the West. FREEDOM!


      Closer yet to folks on the Least Coast will hopefully be Easthampton, Massachusetts, the Amsterdam of the East. FREEDOM!


    2. pot IMPROVES brains says:

      re; the use of cannabis from adolescence to adulthood was associated with slightly lower IQ by age 38.

      and just how do they measure IQ ??

      with tests, just like in school.

      vocabulary, math, ect.

      after being out of school for 20 years, you forget a lot of what you learned then, but have never used, since then.

      a proper test would be; 38 year old pot smokers, tested against 38 year old NON-pot smokers,
      NOT 38 year old pot smokers, tested against their own performance when they were in school, and they still remembered what they just learned.

      we all know that school does not really teach you what you need to know in the real world, working for a living…

      except; school teaches you to show up on time,
      do whatever you are told,
      and wait for the bell to tell you when you can eat,
      and when you can go home.

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