Pubdate: Fri, 29 Apr 2005
Source: New Zealand Herald (New Zealand)
Copyright: 2005 New Zealand Herald
Contact:  http://www.nzherald.co.nz/
Details: http://www.mapinc.org/media/300
Author: Monique Devereux

CANNABIS STUDY FINDS GENE LINKED TO PSYCHOSIS

Some cannabis-using teenagers are highly likely to develop mental health
problems as adults because of their genetic make-up, but most face little
risk, a new study says.

The problems occur for genetically vulnerable adults who used cannabis while
their brains were still developing, and that has prompted researchers to
recommend people "delay onset of use until at least young adulthood".

The finding comes from Otago University's world-renowned study which has
followed 1000 Dunedin-born people for over 30 years.

It says a link between cannabis and mental illness depends on a specific
genetic disposition. But even then, only 15 per cent of the people with the
gene will develop cannabis-related psychotic behaviour, and only if they use
it as adolescents.

Other studies have identified a connection between cannabis and psychotic
behaviour but this research - a combined effort by Otago University,
London's King's College and the University of Wisconsin - has taken it a
step further by pinpointing the exact gene.

The study repeatedly questioned 803 participants in the Dunedin
Multidisciplinary Health and Development Study about their cannabis use when
aged 13, 15 and 18.

When they were 18, 27 per cent said they used cannabis at least once a
month, some every day. By the time they were 26, 3 per cent overall had
developed some recognised psychosis: 1 per cent had schizophrenia and 2 per
cent had milder conditions.

The study defined psychosis as "a period of more than a month in the past
year when the individual constantly experiences hallucinations, delusions,
loss of pleasure, low motivation for normal activities and disorganised
behaviour".

Researchers questioned the 803 study members, and their family and closest
friends.

Among those in the study who used cannabis as teenagers, the rate of
psychosis was 8 per cent. But when broken down further to those who had the
cannabis-vulnerable gene, the rate of psychosis was 15 per cent.

The gene is called COMT and everyone has two copies - one inherited from
each parent - which then develop into one of three different combinations.
The cannabis-vulnerable combination occurs in 25 per cent of the population.

One of the researchers, Associate Professor Richie Poulton of Otago, says
the findings carried an important message for a small part of the
population.

"We are talking about a very real increase in risk but it is constrained to
the minority of people during a particular period of their development."

People should not be alarmist about the findings or "interpret this as
supporting extreme views either that cannabis is extremely harmful or the
reverse.

"Neither position is supported by the facts and people that promulgate those
ideas do the youth of any country a disservice".

In terms of the total population, he said cannabis-related mental illness
was not a major health risk.
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