Cannabis moderately increases the risk of psychosis in young

Cannabis use appears to increase moderately the risk of developing psychotic symptoms in young people, but the effect is greater in those with predisposing factors, shows a prospective cohort study published in the journal "British Medical Journal" .
The risk of developing psychotic symptoms with the use of cannabis is quadrupled in people who already have a vulnerability to psychosis compared with those who did not (23.8% vs. 5.6%), stressed Professor Jim van Os from Maastricht University.

"There is a public health message in there," he said, saying it would be difficult to expect young people all stop smoking cannabis, but they might be aware of the possible adverse effects of this product if you have a family history of psychosis.

The article is based on the following 4 years of a cohort of 2437 young people aged 14 to 24 years, interviewed at the beginning and end of the study by psychologist Cecilia Henquet and his German colleagues from the University of Maastricht for assess the presence of predisposing factors for psychosis, cannabis and other psychotropic substances (alcohol, tobacco, other drugs) and the development of psychotic symptoms.

At the end of follow-up, the overall cumulative incidence in the lives of at least one psychotic symptom was 17.4%.

The analysis of data adjusted for age, sex, socio-economic status, place of residence (urban or rural), the childhood trauma, predisposition for psychosis at baseline and consumption other psychotropic substances, shows that cannabis use (more than 5 times in life) increased by 67% the risk of developing psychotic symptoms in four years compared to people who have never used cannabis.

In addition, it is a dose-dependent relationship with a significant increase of the increased risk of psychotic symptoms from a cannabis once or twice a week. At this frequency, the risk is almost doubled, it is multiplied by 2.44 at a frequency of three to four times per week and 2.23 when consumption is almost daily.

Youth who have predisposing factors for psychosis, the risk of developing four years of psychotic symptoms is increased by 51% with the use of cannabis against an increase of 26% for those who have never smoked, while youth without predisposing factor, the risk is increased by 21% with the use of cannabis against an increase of 15%.

The risk of developing psychotic symptoms with cannabis is so, according to the authors' calculations, 23.8% of young people who have a vulnerability to psychosis, but only 5.6% for those who do not have predisposing factors, a risk multiplied by four.

The researchers speculate that repeated exposure to cannabis may cause an increase in activity of the dopaminergic system and lead to prolonged changes of the endogenous cannabinoid system. These changes are probably more important in adolescents and people with pre-existing vulnerability to dysfunction of the cannabinoid system.