Smoking strong cannabis increases the risk of serious mental illnesses such as psychosis, a study has found.
The study, published in Lancet Psychiatry, found that in London, 21% of new cases of psychosis might be linked to daily cannabis use, and nearly a third 30% to high potency cannabis.
‘Our main findings show that among the measures of cannabis use tested, the strongest independent predictors of whether any given individual would have a psychotic disorder or not were daily use of cannabis and use of high-potency cannabis,’ the authors commented.
‘The odds of psychotic disorder among daily cannabis users were 32 times higher than for never users, whereas the odds among users of high-potency cannabis were 16 times higher than for never users.’
Skunk-like cannabis with a THC content of 14% now makes up 94% of the drug sold on the streets of London. According to the study’s authors, removing strong cannabis from the market would lower London's psychosis incidence rate from 45.7 to 31.9 cases per 100,000 people per year.
‘Our findings confirm previous evidence of the harmful effect on mental health of daily use of cannabis, especially of high-potency types. Importantly, they indicate for the first time how cannabis use affects the incidence of psychotic disorder,’ the authors concluded.
‘Therefore, it is of public health importance to acknowledge alongside the potential medicinal properties of some cannabis constituents the potential adverse effects that are associated with daily cannabis use, especially of high-potency varieties.’