WASHINGTON, Jan. 30 (UPI) -- University of Granada researchers found a person is seven times more likely to experience psychosis after repeated traumatic events through infancy and childhood.
The study, published in the Journal of Psychiatric Research magazine, involved 60 pairs of siblings with one who experiences psychosis and one who has not.
The study also links heavy marijuana use and specific personality traits as factors related to psychosis development.
People who used cannabis more than five times a week are six times more likely to experience psychosis, the study said. Risk also increased in people with an established "neurotic personality," researchers found.
Researchers used McNemar tests and paired-sample tests to determine which traits shared by siblings are associated with psychosis and which are not.
"This work has the value of being the first one in being carried out in a clinical sample of psychotic and non-psychotic siblings," said Manuel Gurpegui and Jorge Cervilla, professors of Pyschiatry at UGR, "and it brings to light the need of the doctors to inquire into these precedents when evaluating their patients."