• Cannabis;
  • psychosis;
  • public mental health;
  • schizophrenia


Aim  To study the role of cannabis use in the onset of symptoms and disorders in the schizophrenia spectrum.

Design  Review of five population-based, longitudinal studies on the relationship between cannabis use and problems ranging from the experience of psychotic symptoms to hospitalization with a confirmed diagnosis of schizophrenia. Several hypotheses are examined that may explain this relationship: (1) self-medication; (2) effects of other drugs; (3) confounding; (4) stronger effect in predisposed people, and (5) etiological hypothesis.

Findings  Hypotheses 1 and 2 can be dismissed; hypothesis 3 is still open to debate, and converging evidence is found for hypotheses 4 and 5—antecedent cannabis use appears to act as a risk factor in the onset of schizophrenia, especially in vulnerable people, but also in people without prior history.

Conclusion  There is an intrinsic message here for public health, but how that message is to be translated into action is not immediately clear.