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SMOKING cannabis has been linked to having a small brain – at least if the dope is taken in large doses, over a long period.

Murat Yücel at the University of Melbourne, Australia, and colleagues scanned the brains of 15 heavy users, who had smoked at least five joints daily for more than 10 years. The volume of their hippocampus, involved in memory and regulating emotion, was on average 12 per cent smaller than non-users, while the amygdala, involved in feeling fear and aggression, was 7.1 per cent smaller (). The cannabis users also scored worse on memory tests and were more likely to suffer from social withdrawal or paranoia.

Since the users’ brains were not measured before they began heavy smoking, no one knows if dope causes the brain to shrink.

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