A POWERFUL “skunk-like” cannabis is associated with one in four new cases of psychosis, a UK study has found.
SCIENTISTS at King’s College London also found the potent form of the Class B drug led to a three-times higher risk of psychosis in casual users, rising to a five-fold risk in those who used it every day.
The findings of the six-year study, published in the Lancet Psychiatry journal, suggest strong forms of cannabis can lead to serious mental illness, the researchers said, as they called for greater public awareness. But it comes as a US neuroscientist suggested long-term recreational cannabis use has no significant association with long-term mental decline. “It is now well known that use of cannabis increases the risk of psychosis,” senior researcher on the study, Professor Robin Murray said. “However, sceptics still claim that this is not an important cause of schizophrenia-like psychosis. “This paper suggests that we could prevent almost one quarter of cases of psychosis if no one smoked high potency cannabis. “This could save young patients a lot of suffering and the NHS a lot of money.” While skunk is associated with psychotic episodes, the milder form of cannabis known as hash has no such link, the scientists say. Dr Marta Di Forti, lead author on the research, said people needed to aware of the risks of smoking strong cannabis. “The results show that psychosis risk in cannabis users depends on both the frequency of use and cannabis potency,” she said. “The use of hash was not associated with increased risk of psychosis. “As with smoking tobacco and drinking alcohol you need a clear public message.” The study looked at nearly 800 people aged between 18 and 65 in south London, including 410 who had suffered psychosis and 370 healthy patients. The researchers highlighted south London had one of the highest recorded rates of psychosis patients and samples of skunk seized in the area had high levels of the chemical tetrahydrocannabinol (THC), the active ingredient in cannabis linked to psychotic episodes such as hallucinations. Meanwhile, speaking at the annual meeting of the American Association for the Advancement of Science in San Jose, Dr Igor Grant, from the University of California, said data pooled from studies involving thousands of participants had failed to demonstrate “meaningful cognitive declines” among recreational users. He added it was important to distinguish between the immediate and long-term effects of drugs such as THC. “Brain imaging has produced variable results, with the best designed studies showing null findings,” he said. “I don’t think there’s any compelling evidence for long-term meaningful effect. Thirty days after smoking, an adult’s memory goes back to normal, as far as these studies show.”