Frequent Marijuana Use Has No Adverse Effects on Brain Structure, Study Finds

The data showed that marijuana use is unrelated to individual differences in brain morphology.

The frequent use of cannabis is not associated with changes in brain structure, according to a new study soon to be published in the scientific journal Addiction.

As part of the study, 20 investigators from 13 institutions across Australia, the United States, and the United Kingdom examined the relationship between frequent marijuana use and brain structure in 1,096 young adults and middle-aged men.

They specifically used MRI scans to assess the relationship between habitual marijuana use and grey matter volumes in seven regions of the brain, including the thalamus, caudate nucleus, putamen, pallidum, hippocampus, amygdala, and nucleus accumbens.

The researchers found no such association between brain morphology and cannabis use.

They concluded that “normal variation in cannabis use is statistically unrelated to brain morphology as measured by subcortical volumes in non-clinical samples.”

The researchers also recorded subjects’ maximum nicotine and alcohol use, and total lifetime multi-drug use. They did find that nicotine was strongly associated with significant decreases in the size of the thalamus in middle-aged males. The thalamus is the part of the brain responsible for relaying sensory signals and the regulation of consciousness, sleep, and alertness.

The findings are significant, considering an earlier troubling study that found evidence of frequent cannabis use being associated with changes in the size and shape of parts of the brain associated with emotion and motivation. This latest study’s findings fail to replicate those, and since then, scientists are now finding those brain changes were most likely caused by other drugs, including alcohol and nicotine.

“This is the largest exploratory analysis integrating brain imaging with self-report cannabis and comorbid substance use data,” the researchers concluded. “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.”

The abstract of study, “Testing associations between cannabis use and subcortical volumes in two large population-based samples,” is now available to access through Wiley Online Library. The full text will soon be published in Addiction.

Similar Findings

The study’s findings are consistent with those of a meta-analysis published earlier this month that found that cannabis exposure in adolescents and young adults is not associated with any significant long-term adverse cognitive performance effects.

Last year, a longitudinal co-twin control study found no link between marijuana use and negative changes in intelligence quotient (IQ) or executive functioning. In a separate study conducted the year before, researchers similarly reported no link between cannabis use and declines in IQ.

The growing body of evidence indicating that cannabis is safe should continue to ease any public health concerns as legalized recreational and medical marijuana continues to expand throughout the U.S.

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