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Psychotic symptoms more likely with cannabis

Michael Le Page and Graham Lawton

New Scientist

Wednesday 01 Dec 2004

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Using marijuana in adolescence and early adulthood can cause psychotic symptoms
later in life, a new study suggests. The risk of developing these symptoms is
"moderate", say researchers, though is higher in people with a pre-disposition
to psychosis.

Up to a third of people develop signs of psychosis at some point during their
lives and several studies have already linked cannabis use with psychotic
symptoms. But it is often difficult to decipher whether cannabis really
triggers psychotic symptoms - such as hearing voices and paranoia - or whether
people with mental health problems are more likely to "self medicate" and use
cannabis.

A team led by Jim van Os of the University of Maastricht in the Netherlands
followed 2437 people aged between 14 and 24. After four years, 21% of cannabis
users had experienced psychotic symptoms compared with 15% of non-users. And
the more a participant used cannabis, the more likely they were to develop
symptoms.


Family history


The risk appears greatest for those with a predisposition to psychosis, as
evidenced by mild signs of psychosis at the outset of the study. Within this
group - about one-tenth of the total - 51% of users experienced symptoms
compared with 26% of non-users.

The definition of psychosis used in the study was very broad, including
occasional symptoms that would not require hospitalisation. Even so, van Os
thinks the results have public health implications. "If you have a personal or
family history of mental illness, you're at risk of negative effects of
cannabis smoking," he says.

Martin Barnes, chief executive of DrugScope in the UK, agrees: "Frequent use, a
predisposition to mental health problems and starting at an early age all
increase the risk of adverse effects. This research underlines that there are
potentially serious health risks associated with cannabis use, particularly for
young people."

Robin Murray of the Institute of Psychiatry in London, UK, notes that cannabis
smoking accounts for about 8% of serious cases of psychosis.

Journal reference: British Medical Journal

 

 

 

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