Skunk cannabis users '18 times more likely to develop psychosis'

People who smoke the strongest form of cannabis - known as skunk - are 18 times more likely to develop psychosis than those who use cannabis resin, say UK psychiatrists.

This is likely to be due to high levels of the psychotic compound delta-9-tetrahydrocannabinol (THC) in skunk, suggest researchers from the Institute of Psychiatry.

For the study, 112 patients with first-episode psychosis and 75 healthy controls screened for psychosis, were questioned about cannabis use.

People who had suffered psychosis were twice as likely to have used cannabis for longer, three times more likely to use it every day and 18 times more likely to use skunk, delegates were told yesterday at the annual meeting of the Royal College of Psychiatrists, held in London.

The potency of skunk has increased from 6 per cent THC in 1995 to the current estimation of 16-18 per cent. But cannabis resin or hash has much lower levels of THC and equal levels of cannabidiol, which has shown to protect users from psychosis and impaired cognition induced by THC.

‘We should have more data on cannabis exposure,' said lead researcher Dr Marta Di Forti. ‘We should take a cannabis history in a more detailed way like we do when we take a history of cigarette smoking to establish risk of lung cancer.

‘But it would be naïve to say that smoking a joint is safe as we do hot have enough data to reach such conclusions.'

Annual Meeting of the Royal College of Psychiatrists Imperial College London

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