Studies: Cannabis Exposure Not Associated With Significant Changes In Brain Morphology

Originally published at blog.NORML.org

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.