Pubdate: Fri, 25 Mar 2005
Source: New Zealand Press Association (New Zealand Wire)
Copyright: 2005 New Zealand Press Association

PRO-CANNABIS LOBBY QUESTIONS RESEARCH LINK TO SCHIZOPHRENIA

A lobby group advocating the legalisation of cannabis, Norml, says it
rejects research that shows some New Zealand teens who used the drug
have an increased risk of developing schizophrenia.

Norml spokesman Chris Fowlie said he was surprised that such a
"sweeping generalisation" could be made from a small sample in the
study, reported this week in New Scientist magazine.

A study of 759 people born in Dunedin in 1972-73, reported a 10 per
cent higher chance of suffering the symptoms of schizophrenia among
those who had smoked cannabis three or more times by the age of
fifteen, compared to those who had not. The team concluded that there
was a vulnerable minority of teenagers for whom cannabis is harmful.

Epidemiologist Mary Cannon of the Royal College of Surgeons in
Ireland, based in Dublin, who helped carry out the New Zealand study,
said her research team believed that cannabis was part of the cause of
schizophrenia.

In the New Zealand study, the number of people who had smoked dope on
three occasions by the age of 15 was just 29, and only three went on
to develop psychosis, but Dr Cannon's research team recently
re-analysed the data from the study to check genetic predisposition to
schizophrenia.

The gene they investigated, called COMT, encodes an enzyme
(catechol-O-methyl transferase) that breaks down a signalling chemical
in the brain called dopamine. COMT comes in two forms, one of which is
marginally more common in people with schizophrenia and is thought to
be a risk factor for the disease. The team found that in New
Zealanders with two copies of the "normal" version of COMT, smoking
cannabis had little effect on their mental health. In people with one
normal and one "bad" form of the gene, smoking cannabis slightly
increased their risk of psychosis.

For people with two copies of the bad gene, cannabis spelled trouble:
smoking it as a teenager increased their likelihood of developing
psychosis by a factor of 10.

But Mr Fowlie said the small number of people in the study who went on
to suffer schizophrenic symptoms raised questions.

"It is simply wrong to claim any sort of result from such a small
number of people," he said.

"In the real world, we can see that cannabis use rates are increasing
throughout western society, and yet rates of mental illness are
falling. "Using cannabis is normal, with 74 per cent of 21-year-olds
in a Christchurch study admitting to using cannabis, and yet we can
see they're not all going insane."
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