Cannabis "increases risk of psychosis"

[abdulhakeem]

Wed 1 December, 2004 16:20

LONDON (Reuters) - Teenagers and young adults who frequently use cannabis are increasing their risk of suffering from psychotic symptoms such as bizarre behaviour and delusions later in life, Dutch scientists say.

Young people with a family history, or pre-existing susceptibility to mental instability, are particularly vulnerable to the negative effects of the drug.

"Cannabis does not act in the same fashion on psychosis risk for everybody. There is a group that is particularly susceptible," Professor Jim van Os, of Maastricht University in the Netherlands, told a news conference on Wednesday.

He and his colleagues studied 2,437 young people aged 14-24 and identified those with a predisposition for psychosis. They also questioned them about their cannabis use and followed them up for four years.

"The results show that in the group without vulnerability to psychosis, there was a small effect of cannabis on the onset of psychotic symptoms four years later," Van Os said.

"But this risk was four times bigger in individuals who had a personal vulnerability to psychosis."

Van Os said the study also showed the odds of experiencing symptoms of psychosis were higher for people who smoked cannabis more frequently.

The findings, which are reported online by the British Medical Journal, are consistent with the results of other studies. Doctors do not understand how cannabis increases the risk of mental illness but they suspect it affects the dopamine system in the brain which is associated with pleasure.


http://www.reuters.co.uk/newsPackageArticle.jhtml?type=topNews&storyID=631275&section=news

[abdulhakeem]

Psychotic symptoms more likely with cannabis

01 December 04
NewScientist.com news service
Michael Le Page and Graham Lawton

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 (online)

http://www.newscientist.com/news/news.jsp?id=ns99996745