People who smoke skunk, the extra strong cannabis grown in hothouse
conditions, are 18 times more likely to develop psychosis that
those who take the milder forms such as hash (cannabis resin), a
new study has found.
The study, which was carried out at the
Institute of Psychiatry and presented this week to delegates at the
Annual Meeting of the Royal College of Psychiatrists, looked at the
links between cannabis use of psychosis.
Psychiatrist Dr Marta Di Forti, as part of the GAP (Genetics and
Psychosis) Study led by Professor Robin
Murray, compared the pattern of cannabis use between 112
patients with first episode psychosis and 75 healthy
‘controls’ screened for
psychosis. Both groups came from the South East London
area.
The researchers found that people who had a
psychotic episode were twice as likely to have used cannabis for longer,
three times more likely to have used it every day and 18 times more
likely to use skunk.
The cannabis plant is "a rich treasure trove
of pharmacology" and contains 60 cannabinoid molecules, said
Dr Paul
Morrison, a senior researcher
working with Prof Murray and presenting at the meeting as
well. The one that has attracted the most publicity is
THC Delta-9- tetrahydrocannabinol, which
is responsible for
the psychotic
symptoms and the cognitive deficits induced by
cannabis.
But cannabis also contains another molecule,
CBD or cannabidiol, which seems to protect users from
the psychosis and impaired
cognition induced by TCH. CBD seems to counteract
the effect of
THC.
The potency of THC in cannabis has increased
steadily over the last decade due to higher concentrations of the
drug and its formulation, delegates at the Annual Meeting
heard.
In 1995, skunk had
6 per cent THC; now that figure is nearer 16 -18 per cent. Skunk not contains only high levels of THC, but
contains no or very
little CBD, so there is nothing to protect users
against its power.
In contrast
with skunk, hash contains much less THC and an almost equal amount of
CBD, which might contribute to further reduce the potency of its
adverse effect. For
example, Savitex, the cannabis drug, used to treat multiple
sclerosis, has equal
amounts of both THC and CBD.
Dr Di Forti used an
analogy comparing users of cannabis to
drinkers. Like the drinker who starts off on half a pint of lager
and ends up drinking a bottle of vodka a day, cannabis users might
start with a weekly joint of hash or grass and graduate to smoking
skunk every day, she said.
Because of the difference in strengths of
cannabis formulations, Dr Di Forti urged psychiatrists to
question their patients on their drug habits in a more detailed
way. "We should have more data on cannabis exposure. We should take
a cannabis history in a more detailed way, like we do when we take a history of
cigarettes smoking to establish risk of lung cancer. But it
would be naive to say that smoking a joint is safe as we do not
have enough data to reach such
conclusion,” she said.
For further information, please contact Liz Fox or Deborah
Hart in the Communications Department.
Telephone: 020 7235 2351 Extensions. 6298 or 6127
References:
Annual Meeting of the Royal College of Psychiatrists, Imperial College, London, 1 - 4 July