Early adolescent cannabis exposure and positive and negative dimensions of psychosis.
OBJECTIVE
To investigate the effect of exposure to cannabis early in adolescence on subclinical positive and negative symptoms of psychosis.


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


METHODS
Government-supported general population cohort study.


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


METHODS
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.


RESULTS
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.
Stefanis
N C
NC
University Mental Health Research Institute, Athens, Greece. nistefan@med.uoa.gr
Delespaul
P
P
Henquet
C
C
Bakoula
C
C
Stefanis
C N
CN
Van Os
J
J
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D017668:Age of Onset; D003430:Cross-Sectional Studies; D005260:Female; D006115:Greece / Q000453:epidemiology; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000453:epidemiology / Q000523:psychology*; D011618:Psychotic Disorders / Q000453:epidemiology / Q000523:psychology*; D012307:Risk Factors; D011795:Surveys and Questionnaires