People who smoke skunk, the most potent form
of cannabis available in UK, are almost seven times more likely to
develop psychotic illnesses like schizophrenia than those who use
traditional hash, according to new
research.
The study, published in the December issue of
the British Journal of Psychiatry,
was carried out by psychiatrists and researchers at the Institute
of Psychiatry, King’s College London (KCL). The team collected
information on cannabis use from 280 people attending South London
& Maudsley NHS Foundation Trust with their first episode of
psychosis. A control group of 174 healthy people from the local
area was also studied.
There was no significant difference between
the two groups in whether they had ever used cannabis, or their age
at first use. However, the patients with psychosis were twice as
likely to have used cannabis for longer than five years, and over
six times more likely to use it every day. Moreover, among those
who had used cannabis, patients with psychosis were almost seven
times more likely to use skunk than the control subjects.
Psychiatrist and lead researcher Dr Marta Di
Forti said: “Patients experiencing their first episode of psychosis
were not more likely to have ever taken cannabis or to have started
doing so earlier than the control group. However, psychosis was
associated with more frequent and longer use of cannabis. Our most
striking finding is that patients with a first episode of psychosis
preferentially used high-potency cannabis preparations of the skunk
variety.”
The researchers believe the high level of
delta-9 tetrahydrocannabinol (Δ9-THC) found in skunk is to blame.
The two main constituents of cannabis are Δ9-THC and cannabidiol.
Δ9-THC is the main psychoactive ingredient, and in experiments has
been shown to produce psychotic symptoms such as hallucinations and
delusions. Cannabidiol does not induce these symptoms and seems to
have anti-psychotic properties – possibly counteracting the effects
of THC. In south-east London, where the study was carried out, the
skunk variety of cannabis contains 12-18% Δ9-THC and less than 1.5%
cannabidiol. In contrast, resin (hash), which was preferred by
cannabis users in the study’s control group, has an average Δ9-THC
of 3.4% and a similar proportion of cannabidiol.
Dr Di Forti concluded: “Our study is the first
to demonstrate that the risk of psychosis is much greater among
people who are frequent cannabis users, especially among those
using skunk, rather than among occasional users of traditional
hash. It is not surprising that those who use skunk daily have the
highest risk of all, because skunk has the highest concentration of
Δ9-THC and a relative lack of cannabidiol with its protective
effect.”
She added: “Unfortunately, skunk is displacing
traditional cannabis preparations in many countries, and the
availability of skunk on the UK ‘street’ market has steadily
increased over the past six years. Public education about the risks
of heavy use of high-potency cannabis is vital.”
The study was funded by the Maudsley Charitable Fund and the
National Institute for Health Research specialist Biomedical
Research Centre for Mental Health at South London & Maudsley
NHS Foundation Trust and KCL.
For further information, please
contact:
Liz Leicester
or Deborah Hart in the Communications
Department.
Telephone: 020 7235 2351 Extensions. 6298 or 6127
References:
Di Forti M, Morgan C, Dazzan P, Pariante C, Mondelli V, Reis Marques T, Handley R, Luzi S, Russo M, Paparelli A, Butt A, Stilo SA, Wiffen B, Powell J and Murray RM (2009) High-potency cannabis and the risk of psychosis, British Journal of Psychiatry, 195: 488-491