A new research paper by Matt Hickman and other researchers from several English universities, highlights that, if cannabis use could trigger schizophrenia, in order to prevent a single such case, ten thousand male cannabis users and thirty thousand female ones would be needed to be taken out of the consumption routine. The figures are half that for the stronger transgenic varieties of cannabis, every day more common, but still totally disproportionate and statistically irrelevant.
Matt Hickman et al., If cannabis caused schizophrenia—how many cannabis users may need to be prevented in order to prevent one case of schizophrenia? England and Wales calculations. Journal for the Study of Addiction, 2009. (paywall)
A divulgative article can be found at Science Daily.
Cannabis consumption may hence very very slightly favor the trigger of such mental problems but it is obviously not any major cause but rather a scapegoat. In my opinion, research should focus on anti-natural birth giving practices instead, which are very likely to cause traumas for all life and may hinder normal development, as well as on exposure to industrial toxins and electromagnetic fields.
Also these kind of studies do not seem to consider the cross influence of other drugs, like LSD,, MDMA, cocaine or alcohol, which also seem to have some psychosis dangers, probably more intense.