We have specific data about this, British scientists warn. In Amsterdam, where marijuana with a high THC content is widely available and is widely used daily, the likelihood of psychotic episodes was nine times higher.
Regular consumption of marijuana causes psychotic disorders, according to the latest study. As much cannabis is enjoyed and as strong as possible, the greater the risk, the British researchers add, warning of new, increasingly potent marihuana types.
In people who consume marijuana daily, there is a three times greater likelihood of developing a psychotic disorder than in people who have never done this. The effects of marijuana on the consumer depend on the amount or strength of the THC contained – with more than ten percent of this psychoactive substance being associated with a five times higher risk.
The study was carried out by researchers at the Royal University in London at eleven locations in Europe – including in Amsterdam, London and Paris – and in the Brazilian city. These days it was published in the prestigious magazine The Lancet Psychiatry.
Over a period of five years, data on more than 1,200 people were analyzed easily and compared with 900 patients who already showed signs of psychosis. They have been found to be more common among marijuana users daily. At the same time, they found that in cities where the use of marijuana is legalized, the rate of psychotic disorders in relation to the rest of the population is higher.
In Amsterdam, where marijuana with a high THC content is widely available to people and is consumed daily by many, the likelihood of psychotic episodes was nine times higher.
The first such study
Researchers emphasized that this is the first study on the impact of cannabis use on the level of psychosis in a wide population. "Since the legal status of cannabis is changing in order to take account of medical conditions, it is also essential for public health to consider its potential adverse effects," said one of the authors of the scandal Marta di Forti.
The use of cannabis has already been decriminalized by many countries. Currently, the use for medical purposes is legal in most European countries, and many are also discussing legalization.
Di Fortiev believes that in Amsterdam, if marijuana with a high THC content is no longer available for sale, the incidence rate of psychosis (per 100,000 population) would drop from 37.7 to 19 per cent.
Robin Murray, a professor and psychiatrist at the University of Glasgow, who also participated in the study, added that marijuana politicians and users should be aware of this. "Fifteen years ago nobody thought that marijuana could have an effect on increasing the risk of developing psychosis, but today we have very concrete data on it" Murray said.