Cannabis users 40% more likely to have psychosis

Cannabis users have a more than 40 per cent increased risk of psychotic illness, new research has warned.

Researchers from leading British universities analysed 35 studies dated up to 2006.

They found that individuals who used cannabis were 41 per cent more likely to have psychosis than those who had never used the drug.

Risk increased with use; the most frequent cannabis users were more than twice as likely to have a psychotic outcome.

Writing in the Lancet medical journal, the researchers claim about 14 per cent of psychotic illnesses in young adults in the UK could be prevented if cannabis was not consumed.

Professor Glyn Lewis from the University of Bristol said the findings made it “appropriate to warn members of the public about the possible risk”.

“It is difficult to be certain about whether cannabis use causes psychotic illnesses such as schizophrenia,” he said. “It is possible that the people who use cannabis might have other characteristics that themselves increase risk of psychotic illness. However, all the studies have found an association.”

Commenting on the report, a spokesperson for the Department of Health (DoH) said the government’s commitment to tackling the problem of cannabis is “unstinting”.

“Our message has always been clear – cannabis is harmful, illegal and should not be taken. Cannabis use, like drug use overall, has fallen in recent years and continues to decline,” the spokesperson added.