Cannabis use and the risk of later schizophrenia

a review

Smit, Filip
Bolier, Linda
Cuijpers, Pim

Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands

Correspondence to: Filip Smit, Trimbos Institute, Netherlands Institute of Mental Health and Addiction, PO Box 725, 3500 AS Utrecht, The Netherlands. Tel: + 31 30 297 1100, Fax: + 31 30 297 1111, E-mail: [email protected]

Submitted 14 July 2003; initial review completed 2 October 2003; final version accepted 5 December 2003

Addiction 99(4):p 425-430, April 2004.

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.