'Skunk' cannabis raises psychosis risk seven-fold

Significantly, cannabis users who smoked skunk were 6.8 times more at risk of being treated in hospital for a psychosis than those who took milder forms of the drug.

Dr Marta Di Forti, from the Institute of Psychiatry in London, who led the research published in the British Journal of Psychiatry, 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 new research involved 280 patients aged 18 to 65 attending a south London hospital with a first episode of psychosis.

The mental health patients were not more likely ever to have used cannabis than healthy participants, and the age at which cannabis users first tried the drug was about the same in both groups.

However, people with psychosis were twice as likely to have used cannabis for longer than five years, and more than six times as likely to take it every day.

Information on this group was compared with data collected from 174 healthy people.

Skunk is a form of herbal cannabis produced by selective breeding that contains high levels of the psychoactive ingredient delta-9 tetrahydrocannabinol.

Previous research has shown that pure tetrahydrocannabinol can induce psychotic symptoms including hallucinations and paranoid delusions.

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