HTTP/1.0 200 OK Content-Type: text/html 006 Study Links Pot-Smoking, Psychosis
Pubdate: Thu, 10 Mar 2005
Source: National Post (Canada)
Copyright: 2005 Southam Inc.
Author: Heather Sokoloff, National Post
Referenced: the study
Related: Psychosis, Hype and Baloney


Heavy pot-smoking has been linked to psychosis in one of the
largest-ever investigations of the long-term health effects of
cannabis use.

Daily marijuana users are 1.6 to 1.8 times more likely to develop
psychosis compared to non-users, a group of New Zealand scientists
reported after following the health and development of 1,200 men and
women born in 1977 for 25 years.

The findings, published in the March edition of the journal Addiction,
make it increasingly difficult for pot advocates to dismiss a growing
body of evidence linking regular cannabis use with increased risks of
psychosis, an outcome mental health experts have long suspected.

"This makes it more definitive," says Harold Kalant, a professor of
pharmacology at the University of Toronto. "Most people accept that
the link has been established beyond anyone's ability to dismiss it."

The New Zealand study also debunks the myth that individuals prone to
psychosis, who may have suffered physical or sexual abuse as children,
would probably attempt to medicate themselves with marijuana.

Instead, the researchers conclude the psychosis in pot smokers is most
likely caused by their daily cannabis use -- and not by other factors.

"The association between cannabis use and psychotic symptoms is
unlikely to be due to confounding factors," wrote researchers David M.
Fergusson and L. John Horwood. "The direction of causality is from
cannabis use to psychotic symptoms."

According to Dr. Kalant, mental health experts have long probed the
question of whether psychosis among pot smokers was caused by
marijuana, or if pot smoking was a form of self-medication among psychotics.

Cases of psychosis which can be attributed to pot smoking tend to show
more "active" symptoms of mental illness, such as delusion and
paranoia, compared to more "passive" symptoms which may have existed
before the marijuana use, such as withdrawal from social interaction,
Dr. Kalant says.

Researchers do not know what it is about marijuana that could cause
psychosis but hypothesize the constant stimulation of the
neurotransmitter dopamine through drug use may have something to do
with it.

"The weight of the evidence clearly suggests that the use of cannabis
may alter underlying brain chemistry and precipitate the onset of
psychosis ... in vulnerable individuals," according to the New Zealand

Study participants reported their marijuana use at age 16, 18, 21 and
25 years. They were also asked to respond to questions about their
mental health, such as whether they heard voices others do not hear,
felt someone else controlled their thoughts or was aware of their
private thoughts, felt something was seriously wrong with their body,
never felt close to another person, felt others cannot be trusted and
felt they were being watched by others.

According to Dr. Kalant, psychosis is basically defined as not being
able to distinguish between reality and fantasy.

"It tends to go with other symptoms like a lot of internal mental
activity of an imaginary nature, paranoid thinking, reverting inward
and, sometimes, aggressive behaviour."

Dr. Kalant says other research is increasingly showing a link between
pot smoking and respiratory and bronchial problems. One recent study,
for example, found two thirds of regular pot-smokers reported chronic
inflammatory problems in their chest.

He says researchers also suspect pot smoking is linked to cancer, just
like tobacco.

"Chemically, tobacco smoking and cannabis smoking are very similar,"
he said. "When people smoke cannabis, with deep breathing and holding
it in the lungs for a long time, they deposit a higher proportion of
tar in the lungs than cigarette smoking."

"There is a logical reason to anticipate cannabis smoking may be
causing serious problems the way tobacco smoke does."

And Dr. Kalant says that just because research has not yet
demonstrated a link between pot use and cancer does not mean it does
not exist, considering it took decades of research to establish the
negative health effects of tobacco smoking. 
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