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16th Jan 2019

Smoking cannabis just once as a teen linked to altering brain structure

'Most people would likely assume that one or two joints would have no impact on the brain.'

Ingesting even a small amount of cannabis as a teenager could have a lasting effect on the brain, scientists have found.

While previous research has been conducted on the effects of heavy cannabis use, this is the first major study to investigate light use in teenagers.

Researchers at Swinburne University in Melbourne looked at 46 14-year-olds from Ireland, England, France and Germany who said they had smoked weed once or twice in the past.

The grey matter volume in these teenagers’ brains was compared to that of teens who had never been exposed to the substance.

The teens who had smoked cannabis had greater amounts of grey matter in the amygdala, the part of the brain thought to process emotion, and the hippocampus, which is associated with memory.

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Grey matter usually decreases in teenage brains, study author Dr Catherine Orr explained.

“During adolescence we lose grey matter in the brain.

“Parts of the brain that are not being used are pruned away and connections between parts of the brain become stronger.

“We think neural pruning may have been disrupted or delayed (in the teens who had smoked cannabis).”

Some people may be more vulnerable to this disruption, she said.

Lead scientist Professor Hugh Garavan added that while they couldn’t be certain, the results implied that even light cannabis use can alter the brain.

“Most people would likely assume that one or two joints would have no impact on the brain,” he said.