- Rebecca Kuepper, research psychologist1,
- Jim van Os, professor1, visiting professor2,
- Roselind Lieb, professor34,
- Hans-Ulrich Wittchen, professor45,
- Michael Höfler, research statistician5,
- Cécile Henquet, lecturer1
- 1Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University Medical Center, Maastricht, Netherlands
- 2King’s College London, King’s Health Partners, Department of Psychosis Studies, Institute of Psychiatry, London, UK
- 3Department of Psychology, Division of Epidemiology and Health Psychology, University of Basel, Switzerland
- 4Max Planck Institute of Psychiatry, Munich, Germany
- 5Institute of Clinical Psychology and Psychotherapy, Technical University Dresden, Germany
- Correspondence to: J van Os, Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University Medical Center, PO Box 616, NL-6200 MD, Maastricht, Netherlands
- Accepted 31 December 2010
Objective To determine whether use of cannabis in adolescence increases the risk for psychotic outcomes by affecting the incidence and persistence of subclinical expression of psychosis in the general population (that is, expression of psychosis below the level required for a clinical diagnosis).
Design Analysis of data from a prospective population based cohort study in Germany (early developmental stages of psychopathology study).
Setting Population based cohort study in Germany.
Participants 1923 individuals from the general population, aged 14-24 at baseline.
Main outcome measure Incidence and persistence of subthreshold psychotic symptoms after use of cannabis in adolescence. Cannabis use and psychotic symptoms were assessed at three time points (baseline, T2 (3.5 years), T3 (8.4 years)) over a 10 year follow-up period with the Munich version of the composite international diagnostic interview (M-CIDI).
Results In individuals who had no reported lifetime psychotic symptoms and no reported lifetime cannabis use at baseline, incident cannabis use over the period from baseline to T2 increased the risk of later incident psychotic symptoms over the period from T2 to T3 (adjusted odds ratio 1.9, 95% confidence interval 1.1 to 3.1; P=0.021). Furthermore, continued use of cannabis increased the risk of persistent psychotic symptoms over the period from T2 to T3 (2.2, 1.2 to 4.2; P=0.016). The incidence rate of psychotic symptoms over the period from baseline to T2 was 31% (152) in exposed individuals versus 20% (284) in non-exposed individuals; over the period from T2 to T3 these rates were 14% (108) and 8% (49), respectively.
Conclusion Cannabis use is a risk factor for the development of incident psychotic symptoms. Continued cannabis use might increase the risk for psychotic disorder by impacting on the persistence of symptoms.
Contributors: H-UW and RL were the principal investigators of the study. RK analysed the data in collaboration with CH, JvO, and MH. RK drafted the paper. All authors contributed to subsequent drafts of the paper and the final version. JvO is guarantor.
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), and this paper is part of NIH grant RO1DA016977-01, PL.
Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisation that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work.
Ethical approval: The EDSP project was approved by the ethics committee of the Medical Faculty of the Technische Universitaet Dresden (No EK-13811).
Data sharing: No additional data available.
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