FRANÇAIS :
Etude transversale auprès de 3500 jeunes grecs de 19 ans : un premier usage avant l'âge de 16 ans est associé à des effets psychotiques plus sévères, indépendamment de la durée de consommation, mais non associé à la dépression.

ENGLISH:
Aims: To investigate the effect of exposure to cannabis early in adolescence on subcIinical 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 3 500 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 con- tributes 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. (Author' s abstract)