Smoking cannabis regularly in young adulthood may alter the shape of the brain, researchers warn this week.
Dr Jodi Gilman and colleagues at Northwestern University and Massachusetts General Hospital, USA, used magnetic resonance imaging (MRI) to compare the brains of 18 to 25-year olds who reported smoking marijuana – or cannabis – at least once per week against those with little to no history of marijuana use.
This showed that the size and shape of two brain regions involved in emotion and motivation were different between the two groups. The nucleus accumbens, which is known to be involved in reward processing, was larger and a different shape and structure among the marijuana users.
Full results are published today (16 April) in The Journal of Neuroscience. The authors say that psychiatric evaluations ruled out the possibility that any of the marijuana using participants were dependent on the drug.
They explain that previous animal studies of tetrahydrocannabinol (THC), the main psychoactive ingredient in marijuana, have found that repeated exposure causes structural changes in similar brain regions. They add that marijuana use is anecdotally linked to problems with motivation, attention, learning, and memory. These new findings suggest that recreational marijuana use may cause brain changes that were previously unidentified.
Dr Gilman calls for more research on the long-term effects of low to moderate marijuana use on the brain.
"This study suggests that even light to moderate recreational marijuana use can cause changes in brain anatomy," she said. “These observations are particularly interesting because previous studies have focused primarily on the brains of heavy marijuana smokers, and have largely ignored the brains of casual users."
Gilman, J. et al. Cannabis Use Abnormalities. Journal of Neuroscience 16 April 2014, volume 34, issue 16, pp. 5529-38.
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