Lame propaganda....
"Cannabis use 'trigger for schizophrenia'"
This explains some of our pro-drug posters.
Lame science, too:
Psychotic symptoms were measured using 10 items from something called Symptom Checklist 90. Participants were asked if they had certain ideas, feelings or beliefs that commonly accompany psychotic states. The researchers did not look at actual diagnoses, and the symptom checklist is not identical to the formal diagnostic criteria listed in the DSM-IV manual. Perhaps most important, they only used 10 "representative" items from a much larger questionnaire.
These 10 items focus heavily on paranoid thoughts or feelings, such as "feeling other people cannot be trusted," "feeling you are being watched or talked about by others," "having ideas or beliefs that others do not share." This presents a big methodological problem, because it is well known that paranoid feelings are a fairly common effect of being high on marijuana.
But the article gives no indication that respondents were asked to distinguish between feelings experienced while high and feelings experienced at other times. Thus, we are left with no indication at all as to whether these supposed psychotic symptoms are long-term effects or simply the normal, passing effects of marijuana intoxication. While it's possible the researchers had these data and didn't see a need to report them, the failure to do so is downright bizarre. It's like reporting that people who go to bars are more erratic drivers than people who don't, without bothering to look at whether they'd been drinking at the time their driving skills were assessed.