High potency cannabis, especially when used daily, is "strongly linked" to the risk of developing psychotic disorders such as schizophrenia and paranoia, scientists said Wednesday.
In Amsterdam and London—where high-THC marijuana has long been the rule rather than the exception—50 and 30 percent of new psychosis cases, respectively, were associated with potent forms of the drug.
The findings, reported
The Lancet, bolster a growing body of research connecting pot to a range of
mental health disorders.
With piecemeal legalisation and decriminalisation, consumption in North America and Europe has increased markedly over the last two decades, even as levels of the drug's mind-bending molecule, delta-9-tetrahydrocannabinol (THC), have risen four- or five-fold.
"The use of cannabis with a high concentration of THC has more
harmful effects on mental health than the use of weaker forms," said lead author Marta Di Forti, a professor at the Institute of Psychiatry, Psychology and Neuroscience at King's College London.
Our findings also indicate for the first time how
cannabis use affects the incidence of psychotic disorder at a population level."
Across 11 European cities or regions, and a 12th in Brazil, one in five new cases of psychosis were associated to daily cannabis use, and one in ten to high potency pot, the study found
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