Pubdate: Thu, 03 Jul 2003
Source: Guardian, The (UK)
Copyright: 2003 Guardian Newspapers Limited
Contact:  http://www.guardian.co.uk/guardian/
Details: http://www.mapinc.org/media/175
Author: Sarah Boseley

CANNABIS LINK TO PSYCHOSIS

Very heavy use of cannabis could be a cause of psychosis, according to a 
leading psychiatrist who believes that society should think carefully about 
the potential consequences of its increasing use.

Robin Murray, professor of psychiatry at the Institute of Psychiatry and 
consultant psychiatrist at the Maudsley hospital in London, says that in 
the last 18 months, there has been increasing evidence that cannabis causes 
serious mental illness. In particular, a Dutch study of 4,000 people from 
the general population found that those taking large amounts of cannabis 
were almost seven times more likely to have psychotic symptoms three years 
later.

"This research must not be ignored," said Professor Murray, speaking at the 
annual general meeting of the Royal College of Psychiatrists in Edinburgh.

Writing in the Guardian last August, Professor Murray said he had been 
surprised that the discussion around cannabis had skirted around the issue 
of psychosis. Psychiatrists had known for 150 years that very heavy 
consumption of cannabis could cause hallucinations and delusions. "This was 
thought to be very rare and transient until the 1980s when, as cannabis 
consumption rose across Europe and the USA, it became apparent that people 
with chronic psychotic illnesses were more likely to be regular daily 
consumers of cannabis than the general population."

In the UK, he said, people with schizophrenia are about twice as likely to 
smoke cannabis. The reason appears to be the effect that the drugs have on 
chemicals in the brain. "In schizophrenia, the hallucinations and delusions 
result from an excess of a brain chemical called dopamine. All the drugs 
which are known to cause psychosis - amphetamine, cocaine and cannabis - 
increase the release of dopamine in the brain."

Cannabis had been the downfall of many a promising student, he suggested. 
"Like any practising psychiatrist, I have often listened to the distraught 
parents of a young man diagnosed with schizophrenia tell me that as a child 
their son was very bright and had no obvious psychological problems. Then 
in his mid-teens his grades began falling. He started complaining that his 
friends were against him and that people were talking about him behind his 
back.

"After several years of increasingly bizarre behaviour, he dropped out of 
school, job or university; he was admitted to a psychiatric unit 
overwhelmed by paranoid fears and persecution by voices. The parents tell 
me that, at some point their son was heavily dependent on cannabis."

It used to be thought that the high numbers of psychotic patients taking 
cannabis could be explained because they used it to alleviate their 
symptoms. The recent studies, however, have looked at large populations 
without mental illness and studied the numbers of cannabis takers within 
them who have developed psychosis.
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MAP posted-by: Larry Stevens