HEAVY MARIJUANA USE SHRINKS BRAIN PARTS

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

Brain scans showed the hippocampus and amygdala were smaller in men
who were heavy marijuana users compared to non-users, the researchers
said. The men had smoked at least five marijuana cigarettes daily for
an average of 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 non-users 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 behaviour,"
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 per cent less and the amygdala volume was seven per cent
less than in 16 men who were not marijuana users, the researchers said.

The researchers acknowledged that the study did not prove it was the
marijuana and not some other factor that triggered these brain
differences. But Yucel said the findings certainly suggested marijuana
was the cause.

While about half of the marijuana users reported experiencing some
form of paranoia and social withdrawal, only one of the non-users
reported such symptoms, Yucel said.

The heavy marijuana users, average age 40, said they had used other
illicit drugs less than 10 times, the researchers said.

A U.S. group supporting legal sales and regulation of marijuana took
issue with the findings, particularly because they were based on men
who were such heavy, long-term users.

"These were people who were essentially stoned all day every day for
20 years," Marijuana Policy Project spokesman Bruce Mirken said by
e-mail. "This study says nothing about moderate or occasional users,
who are the vast majority -- and the (study) even acknowledges this."

"The documented damage caused by comparably heavy use of alcohol or
tobacco is just off-the-charts more serious, and you don't need
high-tech scans to find it," Mirken added.

Yucel said the researchers have begun new research on the effects of
both short-term and long-term and moderate and heavy use of marijuana.