Cannabis Use Unreleated To Previously Reported Neural Changes

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.

However, 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 study of subjects after rigorously controlling for both groups’ use of alcohol. This time, there were 158 participants. As it just so turns out, the two studies were almost completely different.

“This retrospective study examined brain morphology in a sample of adult daily marijuana users versus nonusers. As well as a sample of adolescent daily users versus nonusers. Groups were matched on a critical confounding variable, alcohol use, to a far greater degree than in previously published studies.

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 your brain development. It 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.”

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