VIRGINIA:  The 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 wrote: “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.”

They concluded, “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 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.

A meta-analysis published last week 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.

For more information, contact Paul Armentano, NORML Deputy Director, at: paul@norml.org. Full text of the study, “Testing associations between cannabis use and subcortical volumes in two large population-based samples,” appears in Addiction. NORML’s online fact-sheet, “Marijuana Exposure and Cognitive Performance,” is available online.