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

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 thoughts

  1. Any uncerttainties about this will be resolved when cannabis USE reform is achieved, in the form of ELIMINATING the 500-mg hot burning overdose monoxide Joint which has been providing extracannabinoidal toxicity which should in further studies be “controlled for” as cited in the case of alcohol and tobacckgo use.
    Even children need to learn the 25-mg vape toke technique with long stem oneheaters:
    “Hold flametip 2″ below, suck smoooooooth, slow, don’t start glo0w till after 19 seconds or so.”

  2. Eat yer heart out Dr. Bertha Madras. This is excellent timing for longitudinal data in the Washington v. Sessions case.

    Marijuana consumption stimulates neurogenesis.

    This cellular growth is catalyzed by increased circulation in the brain stem and enhanced even further by unblocking subconscious traumatic barriers through a process called Post Stress Growth (N.P. Heather Manus). Collateral benefits from marijuana for mental development include treatment for undiagnosed symptoms from neurodegenerative disease and increased overall organ function.

    A less celebrated benefit to IQ from regular or even occasional whole plant marijuana consumption is pain-origin identification. At the 2016 SWCannabis Expo in Fort Worth, former Bears Quarterback Jim McMahon described the weeks and months after quitting the “opiate train” the NFL was feeding him and switching to cannabis. “All of the sudden I could feel where the pain was coming from. For once, I wasn’t just an animal taking pills. So I found a specialist and pointed to my neck and sure enough, I had been living with a flipped vertebrae in my neck for years. It was restricting the flow of spinal fluid to my brain, giving me CTE. I was dying slowly. The doctor corrected the problem, I feel great, and used marijuana to heal from the surgery. I continue to use marijuana to heal from the trauma of years of NFL injuries.”

    1. Pain-Origin Identification acronym: POI
      Poi: Hawaiian dish– ground-up TARO root, watered, maybe fermented, baked and pounded to a paste, add usual stuff like salad dressing, ketchup, honey, mustard to taste, another opportunity to introduce, advocate, advertise a medical/edible variant starring our whole plant flower “honey oil” dressing.

    2. @ Julian,
      I love that story about how you were influenced by a movie character played by Morgan Freeman. It’s funny, and yet, for me anyway, kind of heartbreaking, too.

      As amorphous a trait as is an “IQ”, perhaps even harder to quantify is the psychological damage that can be done to a developing mind when it is forced to accept dogma in place of fact, in defiance of the evidence of one’s own senses and even of reason itself.

      I became alienated. I feel conned, and “had.” Sadly, it is true. But, that motivates me to be an activist, at least to “participate in my own liberation.” Or, maybe I’m just in it for a little “payback!”

  3. We still have work to do to break the IQ marijuana-myth among older Americans. Studies such as those from the Salk Institute showing how THC attacks the two proteins that cause alzheimers are one of many collateral benefits of marijuana helping give credibility to these longitudinal studies on teens by breaking down these crusty old marijuana myths. Nothing like a study that affects older people to get older Americans to pay attention to younger ones.

    But the “teenage brain” marijuana myth had to go. For a while I even fell for it. I remember Morgan Freeman in the movie “Lean on Me” slapping the fat kid’s joint out of his mouth saying “It kills ya brain cells son! it kills ya brain cells!” Of course, anyone going to THAT public school would know that’s because the weed was probably laced with crack. But the rest of rural America saw a joint. And now Morgan Freeman smokes weed for his fybromyalgia! What a jip!

    Just my luck when I finally smoked my first joint in high school it actually was laced with crack. (It’s not my fault; I left rural America and went to a D.C. public school for high school). Oddly enough, that primo still kicked my year-old tobacco habit. Even though I wouldn’t smoke another (real) joint until 6 months later, (And never partook of crack again, not even by accident thank God…) suddenly I could taste how awful the cigarettes were and quit cold turkey. Now I don’t care how we measure IQ, THAT $#!+ tried to KILL me! Can’t measure longitudinal IQ when your DEAD!

  4. On a more serious note:

    The Journal of Addiction is a particularly ironic place to put the IQ myth to rest isn’t it? Here we are in the midst of an epic battle over whether we get to call whole plants or synthetic FDA approved toxins “medicine.” And now, during the climax of our American Prohibition Tragedy, we finally get to create a paradigm shift in the very definition of words like “toxic” and “addiction.”

    Whereas the outlawed nontoxic whole plant marijuana is far, far less addictive than the legal, toxic opiate synthetics being prescribed to us at an alarming rate, we must also support institutions that redefine the addictive properties of prohibition itself. I’m serious as Morgan Freeman in Shawshank Redemption when I say this: (Ok, bad allusion, but it was better than when he played God in “Liar, Liar” with Jim Carrey). While it may pass as a lighthearted joke;

    P.U.D.S., or Prohibition Use Disorder Syndrome requires a clinically diagnosed, longitudinal, peer-reviewed study. (ehemm.. subject: the DEA). We cannot defeat the elements of evil in the Controlled Substances Act unless we clearly and legally define the root cause of addiction in our society… addiction which is inherently found in the for-profit-prohibition of any whole plant drugs by tax-subsidized law enforcement.

  5. Marijuana prohibition is a threat to national security. Our government is literally piss testing to disqualify high IQ marijuana employees.

    Don’t believe marijuana increases IQ? Exhibit A: President Trump does not consume marijuana. BAM! His drugs of choice? … oh, a daily dose of artificially inflated ego, greed, avarice with a shampoo bottle of finasteride… don’t seem to help him recognize when his own greed impedes his own personal security. On the other hand, the finasteride shrunk his penis and balls. And apparently his brain: His price demands to lease space for the Secret Service at Trump Tower are so high the SS had to move to a trailer 50 floors below outside the building:

  6. Exhibit B that marijuana prohibition is a threat to our national security: The Secret Service. Gilded by Trump with the loathsome task of defending our masochist-narcissist Ignoramus-in-Chief, the SS has been having a recruitment problem over the last 7 months. That has lead SS policy to relax prior marijuana possession 2 months ago as an impediment to employment on their applications.

    We have witnessed this quality recruitment phenomenon in the tech industry; banning marijuana in Silicon Valley would have meant banning virtually every effective techie all the way back to Steve Jobs. Go ahead. Piss test our Securities and tech firms. Good luck finding talent.

    Take the SS scandal back in 2012 when they got busted in those hotels in Cartegena with some Colombian prostitutes. As it turns out, after Congressional investigation, it was the DEA who lead them to the cartel hookers. The SS was doing coke with Colombian cartels, checking their weapons and briefcases in with hotel management because this was (is) regular DEA practice. The saying was (is) “wheels up, rings off” and besides; coke is out of the system in 72 hours. Marijuana isn’t. And how stupid could the SS be? (Well, aside from that guy who refused to pay his sex worker so she went public). No one was paying attention to the international scrutiny of the US over the made-to-fail drug war from LATAM leaders at the Summit of the Americas during a pivotal time in American polling in support for marijuana legalization because the DEA had effectively changed the subject of media attention to whether some Colombian prostitutes committed sexpionage. Like Trump said about evading taxes by sinking casinos; “Makes me smart, right?” Except our DOJ was caught in bed with the enemy for sex and coke in such a great display of stupidity while the Colombian president discussed medical marijuana legalization with the OAS.

  7. Never has it been made more clear to the intelligence world that the US is piss testing our national security and IQ away through marijuana prohibition. The corruption is so bad the State Department, once a pillar of global diplomacy, has become nothing more than a blank check for the DOJ. Yes, the same DOJ that checks their guns and briefs with disgruntled hotel management while they have coke-sex parties with “criminal” cartels. And Russia is always ready to exploit that weakness.

    But what if the Secret Service smoked weed?

  8. When is the last time America had an honest Attorney General? You have to go back to the early 60’s with Robert F. Kennedy, a man the people loved who was taken out before his sure win in the 1968 presidential election. Instead we got Nixon, all downhill after that.

  9. After using cannabis for 45 years, since age 15, I am 100% certain that I have a higher IQ than President Trump!!! I worked for many years as a computer programmer and electronics technician and I did just fine; better than most!

  10. Agreeing with Miles; I’ve been smoking marijuana quite consistantly since I was 18 and am now 39. The life decisions I am currently making are vastly more intelligent than before I turned 18. I am certain that has much more to do with maturity and a more developed emotional quotient… a degree of intelligence unmeasured by IQ tests…
    At very least I can attest that the entire premise of the New Zealand study… that continued consumption of marijuana from our teens causes a reduction in IQ by age 38… is flawed propaganda and simply untrue.

    Great work by the way, Paul, on your Alternet publication on this subject:

    Sorry Anne Coulter; You’re out of this discussion. If you want to throw around the word “retarded” without peer-reviewed, longitudinal studied facts you have to sit in time out with the rest of the elementary school dunces. This is big-people talk now.

    1. Lol… Bill Maher needs to invite Anne Coulter back on his show so every time she interrupts the other guests can ask her if she needs more pills and crayons… “Yeah, sweetheart, I know, it’s time for your medicine and a good nap. Bill, can you get her a kids menu? And are those crayolas non toxic? (When she gets angry she eats them…)”

  11. 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!

  12. 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.

  13. Hello my name is Thomas Karol , my husband was suffering from liver cancer, and the doctor’s told me that there is nothing they could do to save my beloved husband life. Then a friend told me about hemp oil , i told her that my husband liver cancer was in the last stage that i don’t think the hemp oil will be able to help, and she persuaded me to try, for the love of my husband, i decided to give it a try. I did some research and i found a doctor who helped me with the cannabis oil to cure my husband liver cancer and he assured me that after 3 months the liver cancer will be gone, and For the past one year my husband is perfectly okay and he is free from cancer, if you know any one who is suffering from cancer you can save his/her life by contacting Dr. Brown Nelson via his email : ( it worked exactly as the doctor prescribed. Thanks to Dr. Brown Nelson for taking away sorrow in my life. God will bless Dr. Brown Nelson for helping me with cannabis oil and for his support and care, i will keep on help you to fight cancer in the World, all i have to say is THANK YOU LORD.

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