According to researchers, strong marijuana increases the risk of psychotic episodes

Photo: Graham Dockery

According to a report by researchers at King's College London, the number of people with a first psychotic episode in Amsterdam could be cut in half if potent marijuana is no longer available.

The research, published in The Lancet Psychiatry, states that banning drug races with a high THC content, would reduce the number of episodes for the first time from almost 38 out of 100,000 Dutch to nearly 19.

"If you're a psychologist like me who works in this area and sees psychosis patients in the first episode, it has a significant impact on services and, I would say, on family and society," he says. Marta Di Forti, director research author, told The Guardian.

Cannabis is considered very powerful if it contains more than 10% of the psychoactive substance tetrahydrocannabinol (THC).

The researchers found that the most important link between daily cannabis use and a psychotic disorder was in Amsterdam, where the odds were seven times higher than for those who had never used it.

According to a study conducted by the Dutch Institute for Trimbos Addiction in 2017, the average THC concentration of 17% Dutch marijuana sold in the city's cafes and rises since 2013.