- The Weed Blog https://www.theweedblog.com

Study: Marijuana Use Not Associated With Deficits In Intelligence Quotient


marijuana creativity brainBy Paul Armentano, NORML Deputy Director

Moderate cannabis consumption by young people is not positively associated with changes in intelligence quotient (IQ), according to data presented this week at the European College of Neuropsychopharmacology annual congress in Berlin, Germany.

Investigators at the University College of London analyzed data from 2,612 subjects who had their IQ tested at the age of eight and again at age 15. They reported no relationship between cannabis use and lower IQ at age 15 when confounding factors such as subjects’ history of alcohol use and cigarette use were taken into account.

“In particular alcohol use was found to be strongly associated with IQ decline,” the authors wrote in a press release cited by The Washington Post. “No other factors were found to be predictive of IQ change.”

Quoted in the Independent Business Times, the study’s lead author said: “Our findings suggest cannabis may not have a detrimental effect on cognition, once we account for other related factors particularly cigarette and alcohol use. This may suggest that previous research findings showing poorer cognitive performance in cannabis users may have resulted from the lifestyle, behavior and personal history typically associated with cannabis use, rather than cannabis use itself.”

The investigators acknowledged that more chronic marijuana use, defined in the study as a subject’s admission of having consumed cannabis 50 times or more by age 15, was correlated with slightly poorer exam results at the age of 16 — even after controlling for other variables. However, investigators admitted: “It’s hard to know what causes what. Do kids do badly at school because they are smoking weed, or do they smoke weed because they’re doing badly?”

Commenting on the newly presented data, the meeting’s Chair, Guy Goodwin, from the University of Oxford, told BBC News: “This is a potentially important study because it suggests that the current focus on the alleged harms of cannabis may be obscuring the fact that its use is often correlated with that of other even more freely available drugs and possibly lifestyle factors.”

In a recent review published in the New England Journal of Medicine, the NIDA Director Nora Volkow alleged that cannabis use, particularly by adolescents, is associated with brain alterations and lower IQ. However, the IQ study cited by Ms. Volkow as the basis of her claim was later questioned in a separate analysis published in the Proceedings of the National Academy of Sciences. That paper suggested that socioeconomics, not subjects’ cannabis use, was responsible for differences in IQ and that the plant’s “true effect [on intelligence quotient]could be zero.”

A previous assessment of cannabis use and its potential impact on intelligence quotient in a cohort of young people tracked since birth reported, “[M]arijuana does not have a long-term negative impact on global intelligence.”

Source: NORML - make a donation


About Author

Johnny Green


  1. What I would find interesting is if they could find out if kids who use only alcohol suffer more detriment than kids who use both.

  2. Lets stop criminalizing millions of Americans and wasting billions of our dollars in a futile attempt to eradicate something objectively less harmful than alcohol. Please consider what the following cannabis legalization organizations have to say. Help end this very costly (money is only a small part), harmful, senseless, unjust, unfounded, and more importantly, un-American prohibition by joining their mailing lists, signing their petitions and writing your legislators when they call for it.

    MPP – The Marijuana Policy Project – http://www.mpp.org/
    NORML – National Organization to Reform Marijuana Laws – http://norml.org/
    LEAP – Law Enforcement Against Prohibition – http://www.leap.cc/
    DPA – Drug Policy Alliance – http://www.drugpolicy.org/

  3. Surprise, surprise!! Who would have thunk it? The prohibitionists lied. Oh that’s right, they’ve done that before. So never mind. By the way Cannabis never should have been banned. Stop the lies and legalize. If anybody knows of an updated book to replace “How To Lie With Statistics” by Darrell Huff 1954, please advise. Expect more new Big Lies from the anti-legalization camp and more repeats on the already debunked ones.

  4. I knew that the main study that the Anti crowd cites was flawed and proved absolutely zero negatives.

  5. It’s hard to say. The study wasn’t clinical — cannabis use was self-reported by the subjects with a survey. We won’t really know until someone tries to track down the biological mechanism for the neuroprotective effects of cannabis. My money is on the glial cells, but I’m a gambler.

  6. moretotehstory on

    specifically alcohol is neurotoxic, i wonder if just having thc left over in ones system continues to exhibit a protective effect. Or if one needs to partake first before drinking to get it?

  7. This is what would be expected since cannabis is not toxic to the body and is actually profoundly beneficial via the endocannabinoid system which is central to maintaining homeostasis (health and well being). Alcohol is toxic to the body, damaging cells and the dendrites which connect the brains neurons. This does have profoundly negative effects on cognitive function and intelligence

    Not only is cannabis nueroproctective, but it increases the EQ (empathy quotient) helping the individual to become more compassionate and considerate of the needs of others.” the illegality of cannabis is outrageous, an impediment to full utilization
    of a drug (plant, the herb of herbs) which helps produce the serenity and insight, sensitivity and fellowship so desperately needed in this increasingly mad and dangerous
    world.” –Carl Sagan

Leave A Reply