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Prospective cohort study of cannabis use, predisposition for psychosis, and psychotic symptoms in young people

BMJ 2004; 330 doi: https://doi.org/10.1136/bmj.38267.664086.63 (Published 30 December 2004) Cite this as: BMJ 2004;330:11
  1. Cécile Henquet, research psychologist1,
  2. Lydia Krabbendam, lecturer1,
  3. Janneke Spauwen, research psychologist1,
  4. Charles Kaplan, senior lecturer1,
  5. Roselind Lieb, private lecturer2,
  6. Hans-Ulrich Wittchen, professor3,
  7. Jim van Os, professor (j.vanos{at}sp.unimaas.nl)⇑1
  1. 1 Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University, PO BOX 616, 6200 MD Maastricht, Netherlands,
  2. 2 Max Planck Institute of Psychiatry, Clinical Psychology and Epidemiology Unit, Kraepelinstrasse 2, D-80804 Munich, Germany,
  3. 3 Institute of Clinical Psychology and Psychotherapy, Technical University ofDresden, Chemnitzerstrasse 48, D-01187 Dresden, Germany
  1. Correspondence to: J van Os
  • Accepted 27 September 2004

Abstract

Objective To investigate the relation between cannabis use and psychotic symptoms in individuals with above average predisposition for psychosis who first used cannabis during adolescence.

Design Analysis of prospective data from a population based sample. Assessment of substance use, predisposition for psychosis, and psychotic symptoms was based on standardised personal interviews at baseline and at follow up four years later.

Participants 2437 young people (aged 14 to 24 years) with and without predisposition for psychosis.

Main outcome measure Psychotic symptoms at follow up as a function of cannabis use and predisposition for psychosis at baseline.

Results After adjustment for age, sex, socioeconomic status, urbanicity, childhood trauma, predisposition for psychosis at baseline, and use of other drugs, tobacco, and alcohol, cannabis use at baseline increased the cumulative incidence of psychotic symptoms at follow up four years later (adjusted odds ratio 1.67, 95% confidence interval 1.13 to 2.46). The effect of cannabis use was much stronger in those with any predisposition for psychosis at baseline (23.8% adjusted difference in risk, 95% confidence interval 7.9 to 39.7, P = 0.003) than in those without (5.6%, 0.4 to 10.8, P = 0.033). The risk difference in the “predisposition” group was significantly greater than the risk difference in the “no predisposition” group (test for interaction 18.2%, 1.6 to 34.8, P = 0.032). There was a dose-response relation with increasing frequency of cannabis use. Predisposition for psychosis at baseline did not significantly predict cannabis use four years later (adjusted odds ratio 1.42, 95% confidence interval 0.88 to 2.31).

Conclusion Cannabis use moderately increases the risk of psychotic symptoms in young people but has a much stronger effect in those with evidence of predisposition for psychosis.

Footnotes

  • Contributors H-UW and RL were the principal investigators of the study. CH analysed the data in collaboration with LK, JvO, and JS. CH drafted the paper. All authors contributed to subsequent drafts and the final version. JvO is guarantor for the paper. CK contributed to drafts of the paper and the final version.

  • Funding The EDSP study is funded by grants of the German Ministry of Research, Education and Technology 01EB9405/6 and 01EB9901/6 and the Deutsche Forschungsgemeinschaft (DFG). This paper is also part of NIH-grant “Longitudinal analysis of psychiatric risk factors for SUD” (RO1DA016977-01, PI: E. Costello, HUWittchen Co-PI).

  • Competing interest None declared.

  • Ethical approval The local ethics committee approved the study.

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