Although there is still some controversy around this issue many researchers think that there is a link between cannabis use and psychosis. There is also a link between childhood sexual abuse and psychosis. Some researchers think that all three factors are linked and studies have found that people with psychosis who also use cannabis are significantly more likely to have suffered childhood sexual abuse. Researchers from the University of Ulster and Nottingham Trent University looked at the links between childhood sexual abuse, cannabis use and psychosis in a sample of 5,877 people. The researchers were particularly interested in the order of the link - i.e. did cannabis use come after sexual abuse or vice versa. The study found that sexual trauma with no cannabis use increased the risk of psychosis by a factor of 2.45, cannabis use before sexual trauma increased the risk by a factor of 4.39 and cannabis use after sexual trauma increased the risk 4.25 times.
Shevlin, Mark ... [et al] - Childhood sexual abuse, early cannabis use, and psychosis: testing the effects of different temporal orderings based on the National Comorbidity Survey Psychosis, February 2009, 1(1), 19-28