Cannabis consumption has been shown to have an adverse effect on the course of schizophrenia, with users experiencing more and earlier psychotic relapses, but further studies are needed. At the moment evidence points to cannabis as a vulnerability factor in relation to major mental illness. Cannabis as a risk factor for mental illness. There is some evidence for the idea that the development or recurrence of acute psychosis in the context of cannabis use may be associated with a genetic predisposition to schizophrenia. Among those who have ever taken cannabis, one in ten are at risk of dependence, and the concept of cannabis dependence is at least as valid as that for dependence on alcohol, opiates, stimulants and sedatives.
Men have a higher dependence rate than women.
Cannabis withdrawal syndrome has been identified, with symptoms such as insomnia, feeling nervous and irritable, tremor and nausea. In addition to mental illness increasing a person's vulnerability to cannabis, there is evidence that adolescence is also a vulnerability factor. Adolescents can experience emotional problems that cue cannabis use, which may interfere with learning and personal development and may also lead to use of other drugs. Polydrug use is also common among young people, and this practice may lead to more severe mental health problems than cannabis use alone. Personality may also be another vulnerability factor, and there is a very high incidence of drug misuse among people with antisocial personality disorder.