Early adolescent cannabis exposure and positive and negative dimensions of psychosis

Authors

  • N. C. Stefanis,

    Corresponding author
    1. University Mental Health Research Institute (UMHRI), Athens, Greece,
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  • P. Delespaul,

    1. Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University, Maastricht, the Netherlands,
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  • C. Henquet,

    1. Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University, Maastricht, the Netherlands,
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  • C. Bakoula,

    1. First Department of Paediatrics, Athens University Medical School, ‘Aghia Sophia’ Children's Hospital, Athens, Greeceand
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  • C. N. Stefanis,

    1. University Mental Health Research Institute (UMHRI), Athens, Greece,
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  • J. Van Os

    1. Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University, Maastricht, the Netherlands,
    2. Division of Psychological Medicine, Institute of Psychiatry, London, UK
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Nicholas C. Stefanis
Assistant Professor in Psychiatry University Mental Health Research Institute  (U.M.H.R.I.)
2, Soranou tou Efessiou str.
PO Box 66517
156 01 Papagon
Athens
Greece
Tel: 0030 210 6170003
Fax: 0030 210 6170938
E-mail: nistefan@med.uoa.gr

ABSTRACT

Aims  To investigate the effect of exposure to cannabis early in adolescence on subclinical positive and negative symptoms of psychosis.

Design  Cross-sectional survey in the context of an ongoing cohort study.

Setting  Government-supported general population cohort study.

Participants  A total of 3500 representative 19-year olds in Greece.

Measurements  Subjects filled in the 40-item Community Assessment of Psychic Experiences, measuring subclinical positive (paranoia, hallucinations, grandiosity, first-rank symptoms) and negative psychosis dimensions and depression. Drug use was also reported on.

Findings  Use of cannabis was associated positively with both positive and negative dimensions of psychosis, independent of each other, and of depression. An association between cannabis and depression disappeared after adjustment for the negative psychosis dimensions. First use of cannabis below age 16 years was associated with a much stronger effect than first use after age 15 years, independent of life-time frequency of use. The association between cannabis and psychosis was not influenced by the distress associated with the experiences, indicating that self-medication may be an unlikely explanation for the entire association between cannabis and psychosis.

Conclusions  These results add credence to the hypothesis that cannabis contributes to the population level of expression of psychosis. In particular, exposure early in adolescence may increase the risk for the subclinical positive and negative dimensions of psychosis, but not for depression.

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