29/04/2007 16:00:00
UK: Brain scans pinpoint cannabis mental health risk
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LONDON (Reuters) - Brain scans showing how cannabis affects brain
function may help explain why heavy consumption of the drug triggers
psychosis and schizophrenia in a small number of people, scientists said
on Monday.
Psychiatrists are increasingly concerned about the mental health impact
of smoking large amounts of modern super-strength marijuana, or skunk,
particularly among young people.
Until now, the mechanism by which cannabis works on the brain has been a
mystery but modern scanning techniques mean experts can now detect its
impact on brain activity.
Professor Philip McGuire and Zerrin Atakan of London's Institute of
Psychiatry said their work using magnetic resonance imaging, or MRI,
showed patients given the active cannabis compound tetrahydrocannabinol
(THC) had reduced function in the inferior frontal cortex brain region.
This area is associated with controlling inappropriate emotional and
behavioural responses to situations.
"What THC seems to be doing is switching off that part of the brain, and
that was associated with how paranoid people became," McGuire told
reporters.
Their research will be presented at a two-day International Cannabis and
Mental Health Conference at the Institute of Psychiatry this week.
Similar findings from other teams also highlight the link between THC
dose and the risk of schizophrenia-like symptoms, conference organiser
Professor Robin Murray said.
"It's no longer a contentious issue. The expert community, by and large,
accepts that cannabis contributes to the onset of psychotic symptoms in
general and the severe form of psychosis, schizophrenia," he said.
DOUBLE-STRENGTH JOINTS
One reason for the growing problem is thought to be the increasing
strength of modern strains of cannabis, which are cultivated to produce
the maximum amount of THC.
In recent years, the average THC content of marijuana sold in Britain
has doubled to 12 percent from around 6 percent, while in the
Netherlands it is about 18 percent, Murray said.
Most users of cannabis still do not have a problem with the drug but a
minority, possibly because of genetic factors, are vulnerable to
long-term damage from modern skunk -- which Murray says is to
old-fashioned dope what whisky is to lager.
The rise in THC content is linked with a decline in another active
ingredient called cannabidiol (CBD), since the two products compete
biochemically inside the cannabis plant.
CBD, which reduces anxiety but does not produce the euphoric high of
THC, may help offset some of the paranoid feelings.
Markus Leweke of Cologne University said a clinical trial involving 42
patients showed CBD was as effective as the established medicine
amisulpride, sold as Solian by Sanofi-Aventis, in treating patients with
psychosis.
"It seems there are good guys and bad guys within cannabis," Leweke said.
Source:
http://www.ukcia.org/news/shownewsarticle.php?articleid=12498
Author:
Reuters: UK via UKCIA
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