Heavy marijuana use shrinks brain parts: study

Mon Jun 2, 2008 4:18pm EDT
 

By Will Dunham

WASHINGTON (Reuters) - Long-term heavy use of marijuana may cause two important brain structures to shrink, Australian researchers said on Monday.

Brain scans showed the hippocampus and amygdala were smaller in men who were heavy marijuana users compared to nonusers, the researchers said. The men had smoked at least five marijuana cigarettes daily for on average 20 years.

The hippocampus regulates memory and emotion, while the amygdala plays a critical role in fear and aggression.

The study, published in the American Medical Association's journal Archives of General Psychiatry, also found the heavy cannabis users earned lower scores than the nonusers in a verbal learning task -- trying to recall a list of 15 words.

The marijuana users were more likely to exhibit mild signs of psychotic disorders, but not enough to be formally diagnosed with any such disorder, the researchers said.

"These findings challenge the widespread perception of cannabis as having limited or no harmful effects on (the) brain and behavior," said Murat Yucel of ORYGEN Research Centre and the University of Melbourne, who led the study.

"Like with most things, some people will experience greater problems associated with cannabis use than others," Yucel said in an e-mail. "Our findings suggest that everyone is vulnerable to potential changes in the brain, some memory problems and psychiatric symptoms if they use heavily enough and for long enough."

Among the 15 heavy marijuana users in the study, the hippocampus volume was 12 percent less and the amygdala volume was 7 percent less than in 16 men who were not marijuana users, the researchers said.   Continued...

 
<p>young man smokes marijuana before the 10th annual "Marijuana March" in downtown Toronto May 3, 2008. REUTERS/Mark Blinch</p>