Jason Schiffman, PhD, Associate Professor of Clinical Psychology at the University of Hawaii at Manoa, et al, reported in their article, "Symptoms of Schizotypy Precede Cannabis Use," published Mar. 30, 2005 in Psychiatric Research:

“The onset of schizotypal symptoms generally precedes the onset of cannabis use. The findings do not support a causal link between cannabis use and schizotypal traits.”

Mar. 30, 2005