Conclusion
The observed deleterious effect of cannabis use on the prognosis of patients with psychotic disorder may involve the same mechanism as the observed deleterious effect of cannabis use on the prognosis of individuals with high levels of liability to psychosis. Further study of gene–environment interactions is likely to help elucidate the exact role of cannabis in the onset and the persistence of psychotic disorders, but there is an urgent need for human and animal studies examining the biological mechanisms involved.