Skunk and frequent cannabis use ‘raises psychosis risk’

People who smoke skunk are almost seven times as likely to develop psychotic illnesses as those smoking less potent forms of cannabis, research published today has found.

The study, by the Institute of Psychiatry at King’s College London, also found a link between frequent use of cannabis and psychotic conditions such as schizophrenia.

The research, published in the December issue of the British Journal of Psychiatry, has been described as the first to demonstrate these findings.

Researchers studied 280 people attending South London and Maudsley NHS Foundation Trust with their first episode of psychosis and a control group of 174 healthy people from the local area.

Link with frequent, long-term cannabis use

It found while there was no significant difference between the two groups in whether they had ever used cannabis or their age of first use, 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.

They were also almost seven times more likely to use skunk than control subjects who had used less potent forms of cannabis.

Researchers explained the difference on the basis of variations in levels of delta-9 tetrahydrocannabinol – a psychoactive ingredient of cannabis that has been shown to produce psychotic symptoms such as hallucinations and delusions.

Skunk ingredients

Skunk sold in south-east London contains 12%-18% delta-9 tetrahydrocannabinol while the average for traditional hash was 3.4%.

Psychiatrist and lead researcher Dr Maria Di Forti said: “The availability of skunk on the UK ‘street’ market has increased over the past six years. Public education about the risks of heavy use of high-potency cannabis is vital.”

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