Meta-analysis: Cannabis Exposure Not Associated With Residual Adverse Impact On Cognitive Performance

Cannabis exposure in adolescents and young adults is not associated with any significant long-term detrimental effects on cognitive performance, according to a systematic literature review published today in the journal JAMA Psychiatry.

Investigators affiliated with the University of Pennsylvania, Perelman School of Medicine and with the Children’s Hospital of Pennsylvania reviewed data from 69 separate studies published between 1973 and 2017 involving 8,727 subjects (2,152 frequent or heavy users and 6,575 controls). Researchers reported no significant long-term deficits in memory, attention, or other aspects of cognitive functioning that could be independently attributed to cannabis use, regardless of subjects age of initiation. These findings are in contrast to similar studies assessing the impact of alcohol use and other controlled substances on cognition, which “have shown medium to large effect sizes.”

Authors concluded: “Associations between cannabis use and cognitive functioning in cross-sectional studies of adolescents and young adults are small and may be of questionable clinical importance for most individuals. Furthermore, abstinence of longer than 72 hours diminishes cognitive deficits associated with cannabis use. [R]esults indicate that previous studies of cannabis youth may have overstated the magnitude and persistence of cognitive deficits associated with marijuana use.”

Commenting on the study’s findings, NORML Deputy Director Paul Armentano said: “These conclusions are consistent with those of prior studies – in particular, recent longitudinal twin studies reporting that cannabis use is not independently associated with any residual change in intelligence quotient or executive function. These findings, combined with other recent studies reporting that cannabis exposure appears to have minimal adverse impact on brain morphology — particularly when compared to the dramatic effects of alcohol —dispute the long-standing ‘stoner-stupid’ stereotype. These findings should help to assuage fears that cannabis’ acute effects on behavior may persist long after drug ingestion, or that they may pose greater potential risks to the developing brain.”

Presently, the medical use and dispensing of cannabis is regulated in 30 states. Eight states also regulate the retail sale of cannabis to adults. According to numerous peer-reviewed studies, neither the enactment of medicalization or adult use legalization has been linked to increased marijuana use or access by young people.

Full text of the new study, “Association of cannabis with cognitive functioning in adolescents and young adults: A systematic review and meta-analysis,” appears in JAMA Psychiatry.

15 thoughts

  1. Thanks for spreading the good news about cannabis my friends. We would love to host a conference here in New Orleans.

  2. Wow.
    People have been blaming my shit on cannabis ever since I took my first teenage toke.
    I said, “No, I’ve proved myself. But y’all are driving me crazy!” Weed keeps me sane!

  3. Time to assess the role of what may be the most important toxin associated with marijuana smoking– carbon monoxide– and how an adverse synergy between cannabis and monoxide may have been what led to the development of the “stoner stupid stereotype”.
    Perhaps the “It helps me relax” attitude of some users reflects an underlying fact that carbon monoxide and other combustion toxins produce a relaxation which cannabinoid-assisted euphoria enables them to “enjoy”.

  4. also, can’t post the link, but EVERYONE…..PETE SESSIONS STRUCK AGAIN on Monday…..story online…..Julian, you probably heard…..?¡¿:O closest I could make an angry face to on this TV remote keypad.

  5. Yes, marijuana creates neurogenesis; it does not kill brain cells as Morgan Freeman said as a Principal charachter in the 80s movie “Lean on Me.” (I believed that $#!+… kept me from smokin weed till I was 18! 18!!! … granted the joint was probably laced with crack… a point I tirelessly repeat to the un-urbanized… but boy how a movie can affect a teenager’s brain more than marijuana!)

    I bring this irony up fully aware that the way we joke about marijuana in popular culture… a powerful influence on teenagers… has a profound influence on our perception of how marijuana affects our cognitive dissonance… that is… what we think we know, but as it turns out… the more we think we know we don’t know $#!+:

    That’s right, I just linked an SNL clip where a “mouse that has eaten a ton of marijuana”… a reference to some recent Argentine authorities that tried to explain the disappearance of marijuana in an evidence room… was compared to Miley Cyrus. ?!

    That’s where we are with marijuana jokes? I’m still wondering who still has the low tolerance of weed to end up parked like Cheech and Chong’s Up in Smoke saying “ I don’t think we’re moving”? And that’s all that popular comedy about marijuana from our time and era has to offer? Miley fu€king Cyrus?!!! What ever happened to Dave Chappelle and Bob Sagat in the 90’s movie Half Baked when Sagat stood up and said, “You’re in here (rehab) for marijuana?! I used to suck di€k for €oke!!” Now THAT was classic American comedy.

    We are failing our youth with poor marijuana comedy. If we endeavour to elevate from cognative dissonance, we must continue to declare to our youth the irony that weed resulted in our discovery of beautiful beaches and even ordinary experiences in life, but never Miley Cyrus. And God willing, if we can ever end prohibition, we never have to smoke a surprise joint laced with crack.

    1. In Argentina, I suspect the bandit was El Chapulin Colorado, “The Colorado Grasshopper.” with a name like that? He wants to get caught.

      1. El Chapulin was a beloved Mexican grasshopper, may he rest in peace, but Argentina loved to watch him with the rest of Latin America. Great stuff to watch when youre stoned, but his jokes were straight slapstick family comedy.

        The stuff that influences teens perception of marijuana, at least when teens were watching Half Baked, were clips like this catchphrase;

        “You in here for some marijuana? BOO this man!”

        Still makes me laugh.

      2. Hilarious movie, a personal cult favorite (except, sell-out ending! Boo!)

        I’m a member of AA, a recovering alcoholic, and a stoner, and I agree with the sentiment. But if I am talking to someone who has quit drinking in order to save their life, some of these people are just “done with drugs” or words to that effect, and so while I am honest and forthcoming about how cannabis helps me, even going so far as to recommend it, out of compassion — but I never push anyone who believes that, for them, it might threaten their recovery. Do what you got to do!

        And, nobody is going to “Boo” you at an AA meeting, or throw stuff at you. Not that I’ve ever seen!

        Otherwise, fire one up and let’s watch it again!

      3. Mark,
        I entirely agree; whats good for us may not always be good for others.
        Chapelle’s exaggerated rehab routine made hilarious comedy out of the irony that marijuana is a harmless crutch for rehab when there are real deadly addictions from opioids, heroin, cocaine and meth out there… (“You ever $u€ked di€k for marijuana?! HUNH?!” (Ackward pause…) “No. No, I can’t say that I have.” Lol… Chapelles expression was priceless…)

        But the real irony is not everyone is aware of that irony. They fully believe the mantra of rehab which is why it works for them… even if some rehabs tell them marijuana is dangerous, which it just isn’t.

        I have an old friend I see at poker night once a month who goes to AA and has been off alcohol for 7 years now. And believe me, the world, our roads and blow up dolls in the woods are in a better place for it. I’m not $#!ttin you the thought of this man fallin off the wagon terrifies me. So like any good friend I’m an @$$#ole and drink beer and smoke weed in front of him every time. (Don’t judge me; it’s poker night). So I know he’s stressed out, 4 or 5 kids and all, and every now and then he’ll ask me about weed and I’ll say “of course it helps with stress and anxiety.” But then his AA friends will say “yeah I smoked weed. Two weeks later I was back on the bottle.” He told me he was worried the same would happen to him. I say “Thats funny, I smoke weed on poker night to KEEP from drinking too much… but if that’s how you feel, brother don’t smoke it.”
        And so he did not. And he still doesn’t drink. And somewhere in a tree, there isn’t a naked man with a blow up sex doll, and the world is a better place.

      4. @Julian,
        Yeah, the irony. When I was an actual public menace as a result of my drinking, people saw me as a rising star. We all tried to ignore my problem. But it didn’t go away by denial.

        Now I don’t drink at all, and I’m just a peaceful pot head. “What went wrong?” is the question I get, over and over.

        “Nothing,” I say. “I won! I beat the odds. These are all victory laps for me, now.”

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