CANNABIS USE LINKED TO 40% RISE IN RISK OF SCHIZOPHRENIA

Smoking cannabis increases the risk of schizophrenia by at least 40%
according to research which indicates that there are at least 800
people suffering serious psychosis in the UK after smoking the drug.

Mental health groups called on the government last night to issue
fresh health warnings and launch an education campaign to advise
teenagers that even light consumption of the drug could trigger
long-term mental health problems. The findings came after a rush of
ministers declared their cannabis-smoking pasts and an order from the
prime minister for officials to consider whether the drug should be
reclassified amid fears about its more potent "skunk" form. Last night
the Home Office said the research would be considered in that review.

The study, an analysis published in the Lancet medical journal of
previous research into the effects of the drug on tens of thousands of
people, provides the most persuasive evidence to date that smoking
cannabis can cause mental illness years after people have stopped using it.

The overall additional risk to cannabis smokers is small, but
measurable. One in 100 of the general population have a chance of
developing severe schizophrenia; that rises to 1.4 in 100 for people
who have smoked cannabis.

But the risk of developing other psychotic symptoms among people who
smoke large quantities or are already prone to mental illness is
significant, the researchers say.

People who smoke cannabis daily have a 200% increased risk of
psychosis. They estimate that 14% of 15- to 34-year-olds currently
suffering schizophrenia are ill because they smoked cannabis, a figure
previously thought to be between 8% and 10%. According to the current
diagnosis rates about 800 people would have been spared schizophrenia
if they had not smoked cannabis.

The researchers said the evidence was the strongest yet to show that
cannabis caused psychotic mental illnesses, and not just that people
who were ill smoked more. Dr Stanley Zammit, of Cardiff University,
said: "We think the evidence is such that we need a new official
warning about the risk."

Paul Corry, director of public affairs at the mental health charity
Rethink, echoed calls for more warnings but said it was not evidence
in itself that cannabis should be reclassified. "Rather than focusing
its attention on the reclassification debate, the government would do
well to crack on with the more important job of informing the public
about the health implications," he said.