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Study: Marijuana Use Not Associated With Changes In Brain Morphology


marijuana creativity brainBy Paul Armentano, NORML Deputy Director

It was less than a year ago when the mainstream media was chock-full of headlines like this one: ‘Brain changes associated with casual marijuana use in young adults, study finds.’ The alarmist headlines were in response to a controversial paper published by researchers at Harvard University in Boston and Northwestern University in Chicago which alleged to have found differences in brain morphology in a cohort of 20 college-age marijuana users as compared to 20 non-users. The study’s investigators attributed the differences to subjects’ cannabis use.

But a funny thing happened when a team of scientists from the University of Colorado and the University of Kentucky tried to replicate these results in a separate, larger sample (158 participants) of subjects after rigorously controlling for both groups’ use of alcohol.

They couldn’t.

Writing in the January 28 edition of The Journal of Neuroscience, authors summarized:

“[T]his retrospective study examined brain morphology in a sample of adult daily marijuana users (n = 29) versus nonusers (n = 29) and a sample of adolescent daily users (n = 50) versus nonusers (n = 50). Groups were matched on a critical confounding variable, alcohol use, to a far greater degree than in previously published studies.

We acquired high-resolution MRI scans, and investigated group differences in gray matter using voxel-based morphometry, surface-based morphometry, and shape analysis in structures suggested to be associated with marijuana use, as follows: the nucleus accumbens, amygdala, hippocampus, and cerebellum.

No statistically significant differences were found between daily users and nonusers on volume or shape in the regions of interest. Effect sizes suggest that the failure to find differences was not due to a lack of statistical power, but rather was due to the lack of even a modest effect.”

Why the contradictory results? Investigators speculated that previously reported imaging studies failed to adequately control for the impact of alcohol, a substance that “unlike marijuana, … has been unequivocally associated with deleterious effects on brain morphology and cognition in both adults and adolescents.” In other words, researchers theorized that previously reported differences in the brain images of marijuana consumers as compared to non-users were likely because of subjects consumption of booze, not cannabis.

They concluded, “In sum, the results indicate that, when carefully controlling for alcohol use, gender, age, and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures. … [I]t seems unlikely that marijuana use has the same level of long-term deleterious effects on brain morphology as other drugs like alcohol. The press may not cite studies that do not find sensational effects, but these studies are still extremely important.”

An abstract of the study, “Daily Marijuana Use Is Not Associated with Brain Morphometric Measures in Adolescents or Adults,” is online here.

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Johnny Green


  1. One of the worst effects of amphetamine use is paranoia. I wouldn’t be surprised to learn he’s already a user.

  2. Jordan Shorette on

    Haha if only there was a medication like that in existence lol but you know what the gov says ha crystal meth is safer and less habit forming so maybe kevin sabet should try some meth.

  3. He is mentally ill, and needs medication. I could suggest something that isn’t toxic, has few if any side effects and is entirely natural, but unfortunately, it is still illegal in many places.

  4. Jordan Shorette on

    they should make kevin sabet serve a mandatory minimum see if he changes his ignorant tune, I loathe that human being

  5. Another absurd prohibitionist talking point bites the dust. Kevin Sabet, is anyone still listening to you?

  6. Jordan Shorette on

    so what your really saying is that the whole time those booze guzzling prohibitionists have been saying our brains are fried….lol

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