CANNABIS 'DOUBLES RISK OF PSYCHOTIC ILLNESS'

The strongest evidence of the link between cannabis and serious
mental illness is disclosed today in a study showing the drug is
responsible for one in seven psychotic disorder cases in young
adults.

Those who smoke the drug regularly are more than twice as likely to
suffer illnesses such as schizophrenia, hallucinations and delusions
later in life, scientists found.

The findings from the Government-funded study, published in The Lancet
journal, come only days after a review of the law on cannabis was
ordered, which could see the drug reclassified as Class B.

It was downgraded three years ago to Class C, which carries lesser
penalties for possession and dealing.

Cannabis is the most popular drug in Britain, with 11 per cent of
those aged 16 to 59 saying they had used it in the past year. Up to
one in five young people now reports smoking it at least once a week.
advertisement

In the study, which reviewed 35 studies going back to the 1960s,
researchers found that young people who smoked cannabis were up to 41
per cent more likely to develop a psychotic disorder than those who
had never tried it. The more they smoked, the higher the risk, with
the most frequent users more than twice as likely to have psychotic
experience.

Dr Theresa Moore, from Bristol University, and Dr Stanley Zammit, from
Cardiff University, who carried out the research, said it was vital
that young people were made aware of the dangers.

"We have described a consistent association between cannabis use and
psychotic symptoms, including disabling psychotic disorders," they
said.

"We believe there is now enough evidence to inform people that using
cannabis could increase their risk of developing a psychotic illness
later in life."

In an accompanying editorial, Dr Merete Nordentoft and Dr Carsten
Hjorthaj from Copenhagen University Hospital in Denmark, said that
about 800 cases of schizophrenia in Britain could be prevented every
year if people stopped smoking cannabis.

Mental health charities welcomed the study. "We are extremely
concerned that there is still little known about the effects of
cannabis, especially the stronger strains of the drug, on the
developing teenage brain and it is crucial that more research is
carried out in this area," said Barbara Herts, of the charity, YoungMinds.

"Young people, their parents and the professionals working with them
need to understand the issues surrounding cannabis use and the
potential dangers to their mental health and emotional
well-being."

But Prof Leslie Iverson, from Oxford University, said: "Their
prediction that 14 per cent of psychotic outcomes in young adults in
the UK may be due to cannabis use is not supported by the fact that
the incidence of schizophrenia has not shown any significant change in
the past 30 years."

A report in June showed a dramatic rise in the number being admitted
to hospital because of cannabis.

In only a decade, the number of admissions linked to the drug soared
by 85 per cent, from 510 in 1997 to 946 in 2005-6.

Figures from the National Treatment Agency show that the number
receiving treatment for addiction to cannabis has grown from 13,400 in
2004-2005, excluding the North West, to 22,500 for the first 10 months
of 2006-2007.