CANNABIS 'DISRUPTS BRAIN CENTRE'

Scientists have shown how cannabis may trigger psychotic illnesses
such as schizophrenia.

An Institute of Psychiatry team gave healthy volunteers the active
ingredient tetrahydrocannabinol (THC).

They then recorded reduced activity in an area of the brain which
keeps inappropriate thoughts at bay.

THC levels are thought to have doubled in street cannabis in recent
years - at the expense of other ingredients which may have a
beneficial effect.

A separate study has shown that one of these ingredients - cannabidiol
(CBD) - has the potential to dampen down psychotic symptoms, and could
form the basis of new treatments.

The research will be discussed at a conference on the impact of
cannabis use to be held at the Institute of Psychiatry this week.

Dependency

Although figures are not kept, it is estimated that as many as 500,000
people in the UK may be dependent on cannabis.

Increasing numbers of people are seeking help for cannabis problems at
specialist clinics. In 2005, only heroin users accounted for a greater
proportion of patients.

Experts are concerned that street cannabis is becoming increasingly
potent. It is thought that average THC content has risen from 6% to
12% in recent years.

The Institute of Psychiatry study gave THC, CBD or placebo capsules to
adult male volunteers who had not abused cannabis.

They then carried out brain scans, and a battery of tests, and found
that those who took THC showed reduced activity in an area of the
brain called the inferior frontal cortex, which keeps inappropriate
thoughts and behaviour, such as swearing and paranoia in check.

The effects were short-lived, but some people appeared more vulnerable
than others.

In a second study, a team from Yale University administered THC
intravenously.

Even at relatively low doses, they found 50% of healthy volunteers
began to show symptoms of psychosis.

Volunteers who already had a history of psychotic symptoms appeared to
be particularly vulnerable.

Side Effects

A third study, by the University of Cologne, compared the effect of
CBD and a commonly used anti-psychotic medicine, Amisulpride, on 42
patients with a history of schizophrenia.

After four weeks both groups showed a reduction in psychotic symptoms,
but the CBD group were less prone to side effects, such as muscle
stiffness and weight gain.

The researchers warned that THC and CBD compete with each other
biochemically, so a rise in THC levels would blunt any positive impact
of CBD.

Professor Robin Murray, a consultant psychiatrist at the Institute of
Psychiatry, said the research provided the strongest evidence that
cannabis had a significant impact on the brain.

He said proving a long-term effect was extremely difficult, as it was
not ethical or feasible to stimulate long-term psychosis in volunteers.

However, he said: "If something has an active effect in inducing the
symptoms of psychosis after one dose, then it would not be at all
surprising if repeated use induced the chronic condition."

Professor Murray also warned that the high potency cannabis now widely
available was likely to pose a much bigger risk to health than the
significantly weaker formulations of previous years.

"It is similar to comparing the effect of drinking a glass of wine at
the weekend with drinking a bottle of vodka every day."