Cannabis use and psychosis: the origins and implications of an association

Abstract

Evidence for the effectiveness of treatment or secondary prevention of psychotic illness such as schizophrenia is often disappointing. This situation reflects our limited understanding of the aetiology of psychosis. There is good evidence that both genetic and environmental factors are implicated but the precise identity of these is unclear. Cannabis use is one candidate as a possible, modifiable environmental influence on both incidence and prognosis of psychosis. Evidence supporting this candidature is exclusively observational, and its strength has perhaps been overestimated and problems related to its interpretation underestimated by some. Nevertheless the possibility that cannabis does cause psychosis remains. Because of this, and because there are other good public health reasons to prevent cannabis use, interventions targeting use need to be evaluated. This evaluation, along with other imaginative approaches to future research, is needed to further our understanding of the determinants of mental illness and how we can most effectively improve the population's mental health.