Psychosis among substance users.
This work reviews the evidence that substances of abuse can cause psychosis in nonpsychotic persons. The review is based on the concept that psychosis exists in continuum. Studies examining substance use in, or its effect on, already psychotic individuals were not reviewed. A substantial proportion of substance users experience psychosis. Use of cocaine, amphetamines, cannabis and alcohol seems to be associated with greater risk for psychosis. Severity and duration of use, age at the time of first use and vulnerability to develop psychosis by virtue of familial, possibly genetic and personality factors seem to be the determinants for the development of psychosis. Epidemiological and preliminary biological studies suggest that cannabis is a component cause in the development of schizophrenia. Evidence for the causative role of other substances is less systematic. There exists strong evidence that abuse of substances is associated with greater risk for psychosis and preliminary evidence for their causative role in the development of psychosis. More systematic examination of this issue is likely to throw light on the neurobiology of psychosis and possibly help the vulnerable population in primary prevention.