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Long-term, heavy cannabis use 'alters brain'

03/06/2008

Long-term, heavy cannabis use could result in structural abnormalities in areas of the brain, new research has found.

Scientists at the University of Melbourne and University of Woolongong discovered that people who smoked at least five joints a day for ten years had differences in the areas of the brain thought to be responsible for regulating emotion, memory, fear and aggression.

Cannabis use also was associated with sub-threshold symptoms of psychotic disorders and those using the drug performed significantly worse than non-users on verbal learning.

Using MRI (magnetic resonance imaging) scans the researchers studied the brains of 15 men who smoked more than five joints daily for more than ten years.

They then compared the scans with those of 17 individuals who were not cannabis users.

The hippocampus, thought to regulate emotion and memory, and the amygdala, involved with fear and aggression, tended to be smaller in cannabis users than in controls.

Volume was reduced by an average of 12 per cent in the hippocampus and 7.1 per cent in the amygdala.

"There is ongoing controversy concerning the long-term effects of cannabis on the brain," the authors write in the Archives of General Psychiatry journal.

"These findings challenge the widespread perception of cannabis as having limited or no neuroanatomical [consequences].

"Although modest use may not lead to significant neurotoxic effects, these results suggest that heavy daily use might indeed be toxic to human brain tissue."

The researchers conclude that further research is needed to determine the degree of long-term cannabis-related harm as well as any recovery in brain structure once people stop smoking the drug.