Skunk cannabis use linked to third of psychosis cases

Super-strong “skunk” cannabis may be responsible for a third of cases of psychosis in London, a new study has found.

Smoking highly potent varieties of the drug, which is now the prevalent type on Britain’s streets, raised the risk of conditions such as schizophrenia by five-fold. Researchers at King’s College London estimated that skunk raised the prevalence of psychosis from 31 people in 100,000 to 45.7.

In the catchment area of 500,000 people studied in south London, experts estimated it would account for an extra 60 new cases a year, around three in 10 of the new cases. If extrapolated to the whole of Britain, it could mean hundreds more cases.

Prof Robin Murray, of the Institute of Psychiatry at King’s, said: “As psychiatrists we are overwhelmed by the number of people with psychosis and if there were 30 per cent fewer we would do a better job of looking after them.”

Scientists carried out the study, published in the The Lancet Psychiatry, at 11 sites in five countries across Europe, as well as one in Brazil. They found that the link with psychosis was strongest in London and Amsterdam, where high-potency cannabis is commonly available.

Psychotic conditions such as schizophrenia can have devastating effects, including paranoid delusions and hallucinations. Dr Marta Di Forti, the lead researcher from King’s, added: “Our findings indicate for the first time how cannabis use affects the incidence of psychotic disorder at a population level.

“As the legal status of cannabis changes in many countries and states, and as we consider the medicinal properties of some types of cannabis, it is of vital public health importance that we also consider the potential adverse effects that are associated with daily cannabis use, especially high potency varieties.”

In London, skunk-like cannabis now makes up 94 per cent of the drug sold on the street, according to the study, meaning people would struggle to find a weaker version even if they wanted it.

Dr Adrian James, the registrar at the Royal College of Psychiatrists, said: “Cannabis carries severe health risks and users have a higher chance of developing psychosis.”