Marijuana may increase risk of psychosis Drug makes some users more vulnerable to mental problems Updated: 2:29 p.m. ET Dec. 1, 2004 Teenagers and young adults who frequently use cannabis are increasing their risk of suffering from psychotic symptoms such as bizarre behavior and delusions later in life, Dutch scientists said on Wednesday. Young people with a family history, or pre-existing susceptibility to mental instability, are particularly vulnerable to the negative effects of the drug. â€œCannabis does not act in the same fashion on psychosis risk for everybody. There is a group that is particularly susceptible,â€ Professor Jim van Os, of Maastricht University in the Netherlands, told a news conference. <hr noshade="noshade" size="1">He and his colleagues studied 2,437 young people aged 14-24 and identified those with a predisposition for psychosis. They also questioned them about their cannabis use and followed them up for four years. â€œThe results show that in the group without vulnerability to psychosis, there was a small effect of cannabis on the onset of psychotic symptoms four years later,â€ Van Os said. â€œBut this risk was four times bigger in individuals who had a personal vulnerability to psychosis.â€ Van Os said the study also showed the odds of experiencing symptoms of psychosis were higher for people who smoked cannabis more frequently. The findings, which are reported online by the British Medical Journal, are consistent with the results of other studies. Doctors do not understand how cannabis increases the risk of mental illness but they suspect it affects the dopamine system in the brain which is associated with pleasure. Copyright 2006 Reuters Limited. All rights reserved. Republication or redistribution of Reuters content is expressly prohibited without the prior written consent of Reuters.