London – Daily smoking of very powerful marijuana could multiply by five the risk of developing a psychosis, according to the largest study ever done on the impact of the pot on rates of psychotic disorders.
The research adds to previous studies that revealed links between marijuana and mental health problemsbut still does not specify that marijuana is the cause.
Psychotic disorders – in which people lose touch with reality – are usually triggered by factors such as genetics and the environment. But experts say the findings of the new study have implications for jurisdictions legalizing marijuana, warning them that they should consider the potential impact on their mental health services.
"If we think that there is something special about (high power) cannabis, making the task more difficult, could be a useful measure of harm reduction, "said Suzanne Gage, of the University of Liverpool, who was not associated with the new study.
Researchers from King s College London and elsewhere analyzed data from a dozen sites in Europe and Brazil between 2010 and 2015. About 900 people in whom a first episode of the disease was diagnosed in a mental health clinic, including those with illusions and hallucinations, were compared. with more than 1200 patients in good health. After questioning patients about their use of cannabis and other drugs, the researchers found that daily marijuana use was more common in patients with a first episode of psychosis than in the healthy control group.
The scientists estimated that people who smoked marijuana every day were three times more likely to suffer from a diagnosis of psychosis than people who had never used it. For those who used marijuana every day, the risk was almost five times higher. The newspaper was published online Tuesday by Lancet magazine. It has been paid for by donors, including the British Council for Medical Research, the Sao Paulo Research Foundation and the Wellcome Trust.
"If you decide to use high-alcohol marijuana, keep in mind that psychosis is a potential risk," said Dr. Marta Di Forti, of King's College London. and lead author of the study. She pointed out that the frequency with which people could smoke low-potency marijuana without increasing their risk of psychosis was unknown, but that using it for less than a week seemed to pose no risk.
Di Forti and colleagues estimated that in Amsterdam about half of the new cases of psychosis were associated with smoking high-potency marijuana.
Gage noted that it was possible that people with a family history of psychosis or other risk factors were more likely to develop problems like psychosis or schizophrenia if they used cannabis.
"It could be the thing that tilts the balance for some people," she said. "For them, cannabis could be an additional risk factor, but it certainly would not have to be involved.If you use cannabis, it does not mean that you will definitely develop a psychosis."
It's also possible that people who experience psychotic episodes are more likely to use marijuana, Gage stresses in an editorial accompanying the study. "The study by Di Forti and colleagues questions participants about their use of cannabis before the diagnosis of the first episode of psychosis, but it is possible that subclinical symptoms existed before initiation of cannabis, which means that associations in the opposite direction can not be excluded, "she said. written.
She said that further research would be needed to establish a causal link and determine who might be most likely to risk marijuana for health.
"Given the change the legal status of cannabis Around the world, and given the potential for increased consumption, the next priority is to identify individuals who are at risk of heavy daily cannabis use and to develop educational strategies and interventions to mitigate this risk. risk, "writes Gage.