A study of patients who suffer from psychosis has revealed that nearly a quarter of new cases are linked to the use of strong cannabis.
Researchers at King’s College London found the risk of psychosis to be three times higher for people who smoke potent cannabis, known as ‘skunk’, compared to non-smokers.
People who smoke skunk every day are five times more likely to develop the condition, prompting claims that smoking cannabis is like playing “Russian roulette with your mental health”.
The findings are based on a study of nearly 800 people between the ages of 18 and 65 in south London.
A Home Office spokesman said that the findings support the Government’s approach to drug policy: “Drugs such as cannabis are illegal because scientific and medical evidence demonstrates they are harmful. This report serves to emphasise how they can destroy lives and communities”.
Sir Robin Murray, Professor of Psychiatric Research at King’s College London, criticised those who deny a link between cannabis and mental illness.
He said: “It is now well known that use of cannabis increases the risk of psychosis. However, sceptics still claim that this is not an important cause of schizophrenia-like psychosis.”
Dr Marta Di Forti, the lead author of the research, warned of the increasing availability of skunk, saying: “In London it’s very difficult to find anything else”.
Speaking on BBC Radio 4’s Today Programme, she said: “You’re very likely to get skunk, because there’s no other option”.
Both the Liberal Democrats and the Green Party are pushing for weaker drugs laws.
But Downing Street said last year that any change in drugs policy would “send an incredibly dangerous message to young people”.
Responding to the findings by King’s College London, Marjorie Wallace, chief executive of the mental health charity SANE, said: “While the scientists and politicians debate, we face the daily heartbreak of young people whose minds and thoughts have been altered through continued use and whose families feel helpless.
“What we need is a strong, uncompromising message so that parents, teachers, the police and young people themselves know that a significant percentage who take skunk risk acute, and in some cases lasting, mental illness”.
Mark Winstanley, head of charity Rethink Mental Illness, said: “Essentially, smoking cannabis is like playing a very real game of Russian roulette with your mental health.”
Participants in the south London study included 410 patients who had experienced psychosis and 370 who had not, between 2005 and 2011.