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  • by NORML February 22, 2019

    Cannabis exposure is not associated with significant changes in brain morphology in either older or younger subjects, according to a pair of newly published studies.

    In the first study, researchers from the University of Pennsylvania, Perelman School of Medicine compared brain scans of occasional (one to two times per week) and frequent (more than three times per week) marijuana consumers versus nonusers. Subjects were between 14 and 22 years of age.

    Investigators reported: “There were no significant differences by cannabis group in global or regional brain volumes, cortical thickness, or gray matter density, and no significant group by age interactions were found. Follow-up analyses indicated that values of structural neuroimaging measures by cannabis group were similar across regions, and any differences among groups were likely of a small magnitude.”

    They concluded, “In sum, structural brain metrics were largely similar among adolescent and young adult cannabis users and non-users.”

    The findings appear in the journal Neuropsychopharmacology.

    In the second study, researchers from the University of Colorado at Boulder compared magnetic resonance imaging (MRI) scans in 28 cannabis users over the age of 60 versus matched controls. Cannabis consumers, on average, had used marijuana weekly for 24 years.

    Authors reported that long-term cannabis exposure “does not have a widespread impact on overall cortical volumes while controlling for age, despite over two decades of regular cannabis use on average. This is in contrast to the large, widespread effects of alcohol on cortical volumes) that might be expected to negatively impact cognitive performance.” Researchers also reported “no significant differences between groups” with regard to cognitive performance.

    They concluded: “The current study was able to explore cannabis use in a novel older adult population that has seen recent dramatic increases in cannabis use while controlling for likely confounding variables (e.g., alcohol use). The participants in this study were generally healthy and highly educated, and it is in this context that cannabis use showed limited effects on brain structural measures or cognitive performance.”

    The findings appear in the journal Psychiatry Research: Neuroimaging.

    Commenting on the two studies, NORML Deputy Director Paul Armentano said, “These findings dispute the long-standing ‘stoner-stupid’ stereotype and should help to assuage fears that cannabis’ acute effects on neurocognitive behavior may persist long after drug ingestion, or that cannabis exposure is associated with any sort of significant changes in brain morphology.”

    The studies’ conclusions are similar to those of prior trials similarly finding no significant long-term changes in brain structure attributable to cannabis exposure.

    Full text of the study, “Cannabis use in youth is associated with limited alterations in brain structure,” appears in Neuropsychopharmacology. Full text of the study, “Preliminary results from a pilot study examining brain structure in older adult cannabis users and nonusers,” appears in Psychiatry Research: Neuroimaging.

  • 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 January 2, 2018

    Legalization in DCNeither the occasional nor the heavy use of marijuana by adolescents is associated with decreased motivation, according to clinical data published online ahead of print in the journal Substance Use & Misuse.

    A team of Florida International University researchers assessed the relationship between cannabis use and motivation in 79 adolescent subjects. Participants consisted of both long-term regular consumers and occasional users. Investigators assessed subjects’ motivational tendencies through the use of two validated tools, the Apathy Evaluation Scale and the Motivation and Engagement Scale.

    Authors reported: “After controlling for confounds, no significant differences were observed between regular and light users on any motivation index. Similarly, no associations between motivation and lifetime or past 30-day cannabis use amount were observed.”

    They concluded, “Our findings do not support a link between reduced motivation and CU among adolescents after controlling for relevant confounds.”

    An abstract of the study, “Is cannabis use associated with various indices of motivation among adolescents?”, appears here.

  • 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 July 11, 2017

    marijuana_seedlingAlcohol consumption is associated with negative changes in gray matter volume and in white matter integrity, while cannabis use is not, according to data published online ahead of print in the journal Addiction.

    Investigators from the University of Colorado, Boulder and the Oregon Health & Science University evaluated neuroimaging data among adults (ages 18 to 55) and adolescents (ages 14 to 18). Authors identified an association between alcohol use and negative changes in brain structure, but identified no such association with cannabis.

    “Alcohol use severity is associated with widespread lower gray matter volume and white matter integrity in adults, and with lower gray matter volume in adolescents,” they concluded. By contrast, “No associations were observed between structural measures and past 30-day cannabis use in adults or adolescents.”

    Researchers acknowledged that their findings were similar to those of prior studies “suggesting that regionally specific differences between cannabis users and non-users are often inconsistent across studies and that some of the observed associations may actually be related to comorbid alcohol use.”

    A 2015 brain imaging study published in The Journal of Neuroscience similarly reported that cannabis use was not positively associated with adverse changes in the brain, but that alcohol “has been unequivocally associated with deleterious effects on brain morphology and cognition in both adults and adolescents.”

    Longitudinal data published in June in the British Medical Journal reported, “Alcohol consumption, even at moderate levels, is associated with adverse brain outcomes including hippocampal atrophy.”

    An abstract of the study, “Structural Neuroimaging Correlates of Alcohol and Cannabis Use in Adolescents and Adults,” appears online here.

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