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intelligence quotient

  • 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 Paul Armentano, NORML Deputy Director October 22, 2014

    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.”