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Twin Study: Marijuana Use Has No Direct Effect On IQ

  • by Paul Armentano, NORML Deputy Director January 18, 2016

    personal_cultivationThe cumulative use of cannabis by adolescents has no direct effect on intelligence decline, according to longitudinal data published today in the Proceedings of the National Academy of Sciences.

    Investigators at the University of California, Los Angeles and the University of Minnesota evaluated whether marijuana use was associated with changes in intellectual performance in two longitudinal cohorts of adolescent twins. Participants were assessed for intelligence at ages 9 to 12, before marijuana involvement, and again at ages 17 to 20.

    Researchers reported no dose-response relationship between cannabis use and IQ decline. They also found no significant differences in performance among marijuana using subjects when compared to their non-using twins.

    Investigators concluded: “In the largest longitudinal examination of marijuana use and IQ change, … we find little evidence to suggest that adolescent marijuana use has a direct effect on intellectual decline. … [T]he lack of a dose–response relationship, and an absence of meaningful differences between discordant siblings lead us to conclude that the deficits observed in marijuana users are attributable to confounding factors that influence both substance initiation and IQ rather than a neurotoxic effect of marijuana.”

    The findings follow the publication of a separate longitudinal study in the Journal of Pharmacology which concluded that cumulative adolescent marijuana use is not associated with lower IQ or poorer educational performance once adjustments are made for potential confounders, specifically cigarette smoking.

    An abstract of the study, “Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin studies,” is online here.

    16 Responses to “Twin Study: Marijuana Use Has No Direct Effect On IQ”

    1. Ben says:

      “…lead us to conclude that
      the deficits observed in marijuana users
      are attributable to confounding factors
      that influence both substance initiation and IQ rather”

      In other words, an additional assumed negative
      against cannabis has been debunked.

      We are batting 1000.

    2. Julian says:

      I don’t think this was intentional, but The study says “no increase in intelligence decline,” not what the blog title says, which is “no direct effect on IQ” which is incorrect;

      Marijuana consumption gradually increases IQ.

      When marijuana is consumed in a timely manner early in the morning with excercise, jog ranch or farm work, abstained during study or work until a lunch break, then stay off the herb again until after work, neurogenesis is stimulated and the mind is able to better solve abstract, complex and difficult problems. This is not even factoring improvement to mental faculty calculating prevented mental or neurological disorders. Especially if the boy plays football.

      Nonetheless a vital study to shut the faces up of the prohibitionists that dare stand before us yet.

    3. Julian says:

      What the Hell is this “study”:

      http://www.medicalnewstoday.com/articles/305151.php

      and who the Hell is “Yvette Brazier”?

      This is this biggest load of Crock I’ve read about marijuana and schizophrenia in a long time.

      If you believe you have a hereditary predisposition to schizophrenia, it is recommended to try a strain of marijuana high in non-psychoactive CBD, and keep away from the more common strains high in THC.

      At some point in our culture, we are going to have to recognize that different strains of plants provide diffrent types of medicinal treatment. it’s not that hard. I’m pretty sure we don’t have to make stereotypes about a hundred-million -year-old plant with such a wide variety of chemicals available in its toolbox to heal the human condition.

      This completely irresponsible propaganda I found from Yvette Brazier needs to clarify this fact or stay the hell out of “scientific studies.”

      [Paul Armentano responds: The study in question is preclinical. It assesses THC exposure in rats. I address this study and several relevant human trials specific to cannabis and mental illness here: http://www.alternet.org/drugs/debunking-myth-pot-fries-brain.

    4. Voice of the Resistance says:

      Pop Warner football: HEY KIDS……..

    5. Don M says:

      That marijuana decreases intelligence is just one of the many made up reasons that prohibitionists have been using for decades to support their idiotic platform.

      I wonder how much more it will take to convince people like Kevin Sabet, Chris Christie, and Melinda Haag that they have all been completely wrong all these years… Of course, the sorry b@tch that used to head the DEA, Michele Leonhart, is not capable of logical thought and thus can never be convinced of her stupidity on this subject.

      • Julian says:

        Now what we really need is a study that reveals how sex parties paid for by collusion with Colombian cartels and taxpayer dollars decreases intelligence.
        I mean, c’mon DEA: leaving your briefcases and weapons with disgruntled hotel managers? Then trying to blame it all on the Secret Service and sexpionage? Really?
        Tch* Mm-mm-mm. All that blood money goes straight from the brain to the hip.

    6. Chris Holley says:

      One thing is sure & certain ,whatever president gets marijuana totally legalized,worldwide,will be remembered as the greatest President in history ,same for,states and politicians that help in it’s total success, think bout the history books having your name upheld forever ,never forgotten ….that is for sure and certain ,who will it be though ,you are someone you wish you were ,named welded forever in history books ?

      • Miles says:

        You’re absolutely right! That president will be remembered, by those of us with reasonable intelligence, as one of the greatest presidents ever!

        Foolish perhaps, but I still haven’t given up hope that Obama will be that president. If not, he will simply be remembered as the first black president and that he wasn’t all that different than his white predecessors.

        I’m pretty certain when I say that the primary reason he was elected in the first place, and then for a second term, is because the people believed he was the man to get this done.

        My heart sank to one of it’s lowest level in my life when President Obama laughed off the main question most people wanted to know the answer to in one of his first Q/A sessions with Americans. It felt like a complete betrayal but I know he may not have had much choice considering he was trying to work with a Republican led Congress…

    7. Galileo Galilei says:

      About a decade ago my IQ tested at exactly the same value as it did in kindergarden back in the 1950s

    8. Chris says:

      I never thought that marijuana can actually lover your IQ. I would even say that it can increase knowledge and make your brain open minded.
      I know some people that become dumb after some time, but I think it was because they were not only smoking but drinking heavy and taking other drugs as well.

    9. Miles says:

      You’re absolutely right! That president will be remembered, by those of us with reasonable intelligence, as one of the greatest presidents ever!

      Foolish perhaps, but I still haven’t given up hope that Obama will be that president. If not, he will simply be remembered as the first black president and that he wasn’t all that different than his white predecessors.

      I’m pretty certain when I say that the primary reason he was elected in the first place, and then for a second term, is because the people believed he was the man to get this done.

      My heart sank to one of it’s lowest level in my life when President Obama laughed off the main question most people wanted to know the answer to in one of his first Q/A sessions with Americans. It felt like a complete betrayal but I know he may not have had much choice considering he was trying to work with a Republican led Congress…

      • Julian says:

        I know, I forget this all the time, but Congress has to legalize marijuana if we are to do so permanently. They made this mess with the CSAct, unfortunately we all have to fix it by citizen lobbying and researching our Congressman before voting this November.

        With that said, I suspected since he won the presidency the planets would align for Obama during his last year in office to reschedule (not deschedule as Sanders will) through executive order, right after November elections.The banks are interested, and ready to play. And it would piss off certain Republicans right as he leaves the door. And if he wins his executive decision on immigration in the Supreme Court this summer, Obama will surely be encouraged to make a few more legacy executive decisions after elections and before leaving office.

        This does not mean he will even reschedule, however. President Obama has been doing what he said he would; reducing and pardoning low level drug offenses, ordering the DOJ off of states that have legalized and prettymuch staying out of our way.

        The real question is how many many marijuana legalizing Congressman will Bernie bring to the table?

    10. Mark I. says:

      Elitism is hard to foster when controlling access to safe and effective medication falls upon the individual.

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