Pubdate: Sat, 14 Jan 2006
Source: Guardian, The (UK)
Copyright: 2006 Guardian Newspapers Limited
Contact:  http://www.guardian.co.uk/guardian/
Details: http://www.mapinc.org/media/175
Author: James Randerson, The Guardian
Cited: Advisory Council on the Misuse of Drugs 
http://www.drugs.gov.uk/drugs-laws/acmd/
Cited: Home Office http://www.homeoffice.gov.uk/drugs/
Bookmark: http://www.mapinc.org/find?207 (Cannabis - United Kingdom)
Bookmark: http://www.mapinc.org/people/Charles+Clarke

PANEL SAYS LINK WITH MENTAL ILLNESS IS 'VERY SMALL'

New scientific evidence suggests a causal link between cannabis use 
and long-term psychotic symptoms, according to the government's top 
drug advisory committee. But in a draft report to the home secretary, 
Charles Clarke, seen by the Guardian, the committee says that the 
risks are not high enough to support reclassification as class B.

The report says: "The [committee] considers that cannabis products 
should remain class C. At worst, the risk to an individual of 
developing a schizophreniform illness as a result of using cannabis 
is very small. The harmfulness of cannabis, to the individual, 
remains substantially less than the harmfulness caused by substances 
currently controlled under the act as class B." A source close to the 
committee said only one member out of 36 voted to shift cannabis back 
to class B.

The report said: "Collectively, the weight of evidence from these 
studies suggests an association between cannabis use, and the 
development of schizophrenia or a schizophreniform disorder, that is 
causal ... The best current estimate of the populations-attributable 
risk of schizophreniform illness due to cannabis (the percentage 
reduction in the prevalence of the condition if the use of cannabis 
could be totally eliminated) is about 8-10%." In March, Mr Clarke 
asked the Advisory Council on Misuse of Drugs (ACMD) to look at the 
decision to declassify cannabis from B to C and consider evidence 
that cannabis available in Britain is increasing in potency. He 
directed it to two recent population-based studies suggesting a link 
between cannabis use and mental health problems.

On the potency question, the ACMD concluded: "There is no evidence 
that, during this period [1995-2005], the potency of cannabis resin 
has changed in any significant way ... There has, however, been an 
increase in the potency in sinsemilla." This refers to intensively 
grown super-strength varieties such as skunk.

Since 2002 a handful of population-based studies have pointed to 
cannabis being a causal factor in schizophrenia and the development 
of more subtle psychotic symptoms.

"Each one of these studies has its own deficiencies, but the 
impressive thing is that they all point in the same direction," said 
Robin Murray, a psychiatrist at King's College London who wrote some 
of the papers. They suggest that cannabis increases the chance of a 
user developing psychotic symptoms two-or fourfold, he said. The risk 
of lung cancer for cigarette smokers is 10-15 times.

He believes that reclassifying cannabis was a mistake, but he accepts 
that the scientific case is far from watertight. Cannabis use and 
schizophrenia could be linked by a third factor, perhaps cannabis 
users being more likely to use another drug that causes mental health 
problems, something the new studies try to take into account.

Others are sceptical of the new studies. "The total number of people 
involved is very, very small," said Professor Leslie Iversen, a 
pharmacologist at Oxford University and ACMD member. "If you look at 
any of those studies, a very tiny proportion of the cohort actually 
develop psychotic illness that might be attributable to cannabis."

Research by Cecile Henquet and her colleagues at the University of 
Maastricht was also considered by the council. "The consensus is that 
cannabis is not harmless. It is much more harmful than we expected, 
but it is not that cannabis in itself can cause psychosis," she said. 
"Apparently some people have a sensitive brain to cannabis exposure."

GROUP TRIALS

Study group: Swedish army conscripts

Size: Around 50,000

When: Originally 1988, but updated in 2002

Finding: Heavy cannabis users at 18 years old were 6.7 times more 
likely than non-users to be diagnosed with schizophrenia 27 years later.

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Study group: Netherlands Mental Health Survey

Size: Around 4,000

When: 2002

Finding: Cannabis users nearly three times more likely to experience 
psychotic symptoms 3 years later.

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Study group: New Zealand cohort studied for 20 years

Size: Around 1,000

When: 2003

Finding: Users dependent on cannabis at 18 were 3.7 times more likely 
to get psychotic symptoms.

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Study group: Individuals born in Dunedin, New Zealand

Size: Around 750

When: 2002

Finding: 10.3% of cannabis users aged 15 were diagnosed with 
schizophrenia-like conditions at 26, against 3% of non-users.
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MAP posted-by: Richard Lake