Cannabis use and the risk of later schizophrenia: a review.
OBJECTIVE
To study the role of cannabis use in the onset of symptoms and disorders in the schizophrenia spectrum.


METHODS
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.


RESULTS
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.


CONCLUSIONS
There is an intrinsic message here for public health, but how that message is to be translated into action is not immediately clear.
Smit
Filip
F
Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands. fsmit@trimbos.nl
Bolier
Linda
L
Cuijpers
Pim
P
D017668:Age of Onset; D002188:Cannabis / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects*; D011605:Psychoses, Substance-Induced / Q000209:etiology*; D012307:Risk Factors; D012559:Schizophrenia / Q000139:chemically induced*