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intelligence

  • 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.”

  • by Paul Armentano, NORML Deputy Director August 30, 2012

    The mainstream press has been abuzz in recent days regarding the findings of a recent study suggesting that early-onset, persistent cannabis exposure by those under age 18 could potentially pose adverse effects on intelligence quotient.

    Yet, absent from the media’s discussion of the study — a discussion that has even included some fairly critical reviews of the study’s methodology (See here and here for just two examples.) — is any talk of the role that marijuana prohibition plays in inadvertently steering young people toward cannabis, an issue I address in depth in a column published today and excerpted below:

    Pot & IQ: A Flawed Debate
    via hightimes.com

    [excerpt] Even if one is to accept the study’s findings at face value, it’s hard to see how concerns regarding the potential impact of cannabis on the developing adolescent brain are any way a persuasive argument in support of present day marijuana prohibition. After all, virtually no one wants kids as young as 12 or 13 years of age consuming a mood-altering substance like cannabis. Yet, under cannabis criminalization – a policy that prohibits its use for people of all ages and compels all consumers to acquire the product on the black market instead of from licensed businesses – teens are more likely to have easy access to pot, not less.

    … Specifically, a June 2012 study by the Centers for Disease Control reported that more teens are smoking pot than cigarettes.

    Not so coincidentally, teens’ declining use of cigarettes has run parallel to increased state and federal efforts to penalize those licensed businesses that improperly sell to minors and to educate the public about the health risks associated with tobacco. Ditto for booze.

    In short, it’s legalization, regulation, and public education – coupled with the imposition and enforcement of appropriate age restrictions – that most effectively keeps mind-altering substances out of the hands of children and reduces the likelihood of their abuse.

    Isn’t it about time we took this same approach for pot?

    You can read the full essay and comment on it here.

  • by Paul Armentano, NORML Deputy Director July 27, 2011

    [Editor’s note: This post is excerpted from this week’s forthcoming NORML weekly media advisory. To have NORML’s media alerts and legislative advisories delivered straight to your in-box, sign up here.]

    The consumption of cannabis, even long-term, poses few adverse effects on cognitive performance, according to clinical trial data to be published in the scientific journal Addiction.

    Investigators at the University of Melbourne and the Australian National University, Center for Mental Health Research assessed the impact of cannabis use on various measures of memory and intelligence in over 2,000 self-identified marijuana consumers and non-users over an eight-year period. Among cannabis consumers, subjects were grouped into the following categories: ‘heavy’ (once a week or more) users, ‘light’ users, ‘former heavy’ users, ‘former light’ users, and ‘always former’ — a category that consisted of respondents who had ceased using marijuana prior to their entry into the study.

    Researchers reported: “Only with respect to the immediate recall measure was there evidence of an improved performance associated with sustained abstinence from cannabis, with outcomes similar to those who had never used cannabis at the end point. On the remaining cognitive measures, after controlling for education and other characteristics, there were no significant differences associated with cannabis consumption.”

    They concluded, “Therefore, the adverse impacts of cannabis use on cognitive functions either appear to be related to pre-existing factors or are reversible in this community cohort even after potentially extended periods of use.”

    Separate studies have previously reported that long-term marijuana use is not associated with residual deficits in neurocognitive function. Specifically, a 2001 study published in the journal Archives of General Psychiatry found that chronic cannabis consumers who abstained from the drug for one week “showed virtually no significant differences from control subjects (those who had smoked marijuana less than 50 times in their lives) on a battery of 10 neuropsychological tests. … Former heavy users, who had consumed little or no cannabis in the three months before testing, [also] showed no significant differences from control subjects on any of these tests on any of the testing days.”

    Additionally, studies have also implied that cannabis may be neuroprotective against alcohol-induced cognitive deficits. A 2009 study by investigators at the University of California and San Diego reported that binge drinkers who also used cannabis experienced significantly less white matter damage to the brain as compared to subjects who consumed alcohol alone.

    For more information regarding the impact of cannabis on brain function, see NORML’s factsheet ‘Cannabis and the Brain: A User’s Guide,’ here.