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.