Loading

IQ

  • by Paul Armentano, NORML Deputy Director April 30, 2018

    Marijuana researchThe frequent use of cannabis is not associated with changes in brain structure, according to data published online ahead of print in the journal Addiction.

    An international team of scientists from Australia, the United Kingdom, and the United States assessed the relationship between habitual cannabis exposure and grey matter volumes in seven regions of the brain – including the thalamus, hippocampus, amygdala, and the nucleus accumbens – in two large population-based twin samples.

    Researchers reported, “[N]ormal variation in cannabis use is statistically unrelated to individual differences in brain morphology as measured by subcortical volume.”

    By contrast, the repeated use of nicotine was positively associated with significantly smaller thalamus volumes in middle-aged males.

    Authors concluded: “This is the largest exploratory analysis integrating brain imaging with self-report cannabis and comorbid substance use data. After correcting for multiple testing, there was no effect of cannabis use on the volume at any subcortical region of interest in young adults or middle-aged males. … In the context of expanding medicalization and decriminalization and the concerns surrounding the consequences of increased cannabis availability, our findings suggest that normal variation in cannabis use is statistically unrelated to brain morphology as measured by subcortical volumes in non-clinical samples.”

    The findings are consistent with those of prior brain imaging studies reporting that cannabis exposure appears to have little to no significant adverse impact upon brain morphology — particularly when compared to the dramatic effects associated with the alcohol exposure.

    The study’s findings fail to replicate those of a well-publicized 2014 paper which alleged that even casual marijuana exposure may be linked to brain abnormalities, particularly in the amygdala.

    Last week, a meta-analysis of 69 separate studies reported that cannabis exposure in adolescents and young adults is not associated with any significant, residual detrimental effects on cognitive performance. The results from a pair of recently published longitudinal twin studies similarly report that cannabis use is not independently associated with any residual change in intelligence quotient or executive function.

    An abstract of the study, “Testing associations between cannabis use and subcortical volumes in two large population-based samples,” appears online here.

  • by Justin Strekal, NORML Political Director August 22, 2017
    Photo Credit: Carlo Allegri

    Photo Credit: Carlo Allegri

    Giving remarks to the Native American Housing Association, Housing and Urban Development Secretary Ben Carson strayed into the marijuana reform debate. Unfortunately, the doctor did not know his facts.

    Per the Flathead Beacon:

    The HUD secretary briefly strayed from his prepared remarks to note that he believed marijuana use was just as problematic as opiate abuse.

    “I’m not all that enthusiastic about marijuana because there have been numerous studies that show exposing a developing brain to marijuana can lead to lower IQs,” he said. “We already have enough people with a low IQ, and we don’t need anymore.”

    The ongoing stereotype of marijuana consumers may be funny in movies, but it runs counter to evidence based science.

    NORML has reported on three studies over the last year and a half that have come out dispelling this myth.

    In London, United Kingdom, researchers concluded, “In summary, the notion that cannabis use itself is causally related to lower IQ and poorer educational performance was not supported in this large teenage sample.”

    Data published in the Proceedings of the National Academy of Sciences led researchers to conclude: “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.”

    Researchers published in the journal Addiction 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, and here– finding that cannabis use alone during adolescence does not appear to have a significant, direct adverse effect on intelligence quotient.

    Further, as to Secretary Carson’s remarks in the context of the nations opioid epidemic, it is important to note that medical marijuana access is associated with reduced rates of opioid use and abuse, opioid-related hospitalizations, opioid-related traffic fatalities, and opioid-related overdose deaths.

    Don’t let those who speak in outdated rhetoric fool you. Stay vigilant against those who maintain the systems of prohibitionist oppression.

    Click here to tell your member of Congress to join the newly formed Congressional Cannabis Caucus, to find real policy solutions to reforming our nations marijuana laws in our quest to deschedule the plant. 

  • 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 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.

  • by Paul Armentano, NORML Deputy Director January 12, 2016

    cropsMarijuana use by adolescents is not associated with lower IQ or poorer educational performance once adjustments are made for potential confounders, specifically cigarette smoking, according to longitudinal data published online ahead of print in the Journal of Psychopharmacology.

    British investigators assessed the relationship between cumulative cannabis use and IQ at the age of 15 and educational performance at the age of 16 in a cohort of 2,235 adolescents.

    After researchers adjusted for potentially confounding variables, such as childhood depression and cigarette use, they reported, “[T]hose who had used cannabis [greater than or equal to] 50 times did not differ from never-users on either IQ or educational performance.”

    By contrast, teen cigarette smoking was associated with poorer educational outcomes even after researchers adjusted for other confounding variables.

    Researchers concluded, “In summary, the notion that cannabis use itself is causally related to lower IQ and poorer educational performance was not supported in this large teenage sample.”

    A widely publicized New Zealand study published in 2012 in The Proceedings of the National Academy of Sciences reported that frequent use of cannabis by those under the age of 18 was associated with lower IQ by age 38. However, a separate review of the data published later in the same journal suggested that the changes were likely the result of socioeconomic differences, not cannabis use.

    More recently, the results of a 2015 study in the journal Drug and Alcohol Dependence reported that the effects of persistent adolescent cannabis use on academic performance “became non-significant after controlling for persistent alcohol and tobacco use.”

    Full text of the study, “Are IQ and educational outcomes in teenagers related to their cannabis use? A prospective cohort study,” appears online here.

Page 1 of 212