Three hypotheses explain the association between cannabis and schizophrenia: cannabis can trigger schizophrenia, cannabis is used to mitigate schizophrenia symptoms, and common factors account for the association. Biological and genetic factors dominate research, while social and cultural contributions are underexplored. Evidence for cannabis as a causal factor for schizophrenia has not been established. Research must extend beyond males from western countries to advance understanding.
Research on the link between cannabis use and psychotic symptoms has advanced over four decades but remains complex. While some insights into the nature of this relationship have been gained, major gaps persist in understanding the full trajectory of cannabis psychosis. Treatment options are limited, and there is little evidence to reliably predict who is at risk, which could enable early intervention to reduce incidence, though complete elimination is unrealistic.
A dose-response relationship exists between cannabis use and psychosis, and for individuals with schizophrenia, cannabis worsens their symptoms. These findings support a multi-causal model where vulnerability interacts with a precipitating agent to produce disease. Although this model is common in epidemiology, communicating it has been difficult because the increased risk at the population level is weak and the vulnerabilities are rare, and because people bring strongly held preconceptions to interpreting complex multi-causal phenomena.