LONDON, England, Wednesday February 25, 2015 – A major new study has concluded that about a quarter of new cases of psychotic conditions such as schizophrenia could be the direct result of smoking potent varieties of marijuana.
The findings of the six-year study suggest that about 60,000 people in Britain are living with conditions involving paranoid episodes and hallucinations brought on by abuse of super strong cannabis, known as skunk. Over 300,000 people who have smoked skunk will experience such problems in their lifetime, moreover.
The study, by researchers from the Institute of Psychiatry, Psychology & Neuroscience at King’s College London, calculates that daily users of skunk are five times more likely to suffer psychosis than those who never touch it.
These findings reopen the debate about the classification of cannabis as an illegal drug, with some supporters of liberalisation now considering tougher restrictions on some varieties.
Britain’s Justice Secretary Chris Grayling said the findings underlined arguments against decriminalisation.
The Kings College researchers studied almost 800 working-age adults from one area of south London, half of whom had been recently treated for a psychotic episode for the first time.
In that area, the incidence of schizophrenia has doubled since the mid-sixties, a trend widely thought to be linked to drug use.
While marijuana use in the UK overall has fallen by about 40 percent in the past decade, the typical potency has increased sharply over that period for those still using it.
Levels of the main psychoactive compound tetrahydrocannabinol (or THC) are about 15 percent in skunk, compared with about four per cent in traditional “hash.”
Researchers found that the strength of cannabis and the frequency of use played a crucial role in determining the mental health risks.
“Compared with those who never used cannabis, individuals who mostly used skunk-like cannabis were nearly twice as likely to be diagnosed with a psychotic disorder if they used it less than once per week, almost three times as likely if they used it at weekends, and more than five times as likely if they were daily users,” the paper noted.
Skunk use was found to be the “strongest predictor” of psychotic illness in those studied, with 24 percent of new cases in the area attributable to skunk.
Those who started smoking cannabis before the age of 15 were also found to have a higher risk of developing psychotic disorders than others.
“Our findings show the importance of raising public awareness of the risk associated with use of high-potency cannabis, especially when such varieties of cannabis are becoming more available,” the paper said.
“The worldwide trend of liberalisation of the legal constraints on the use of cannabis further emphasises the urgent need to develop public education to inform young people about the risks of high-potency cannabis.”
Lead author Dr Marta Di Forti said the significance of how regularly people smoked cannabis has often been overlooked in day-to-day treatment.
“When a GP or psychiatrist asks if a patient uses cannabis it’s not helpful – it’s like asking whether someone drinks,” she pointed out. “As with alcohol, the relevant questions are how often and what type of cannabis.”
Sir Robin Murray, professor of psychiatric research at King’s College, 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.
“This paper suggests that we could prevent almost one quarter of cases of psychosis if no-one smoked high potency cannabis.”
The findings of the study come at a time when it is believed that more potent varieties of marijuana, some of them more than twice as strong as those currently available, have been developed in the Netherlands.