C├ęcile Henquet, PhD, Researcher in the Department of Psychiatry and Neuropsychology at Maastricht University, et al., in their Dec. 2004 article "Prospective Cohort Study of Cannabis Use, Predisposition for Psychosis, and Psychotic Symptoms in Young People," published in the British Medical Journal, stated:

“Exposure to cannabis during adolescence and young adulthood increases the risk of psychotic symptoms later in life. Cannabis use at baseline increased the cumulative incidence of psychotic symptoms at follow up four years later… but has a much stronger effect in those with evidence of predisposition for psychosis.”

Dec. 2004