Cannabis use predicts future psychotic symptoms, and vice versa.
OBJECTIVE
To assess if cannabis use is a risk factor for future psychotic symptoms, and vice versa, in adolescents and young adults from the general population.


METHODS
Cohort study.


METHODS
'Zuid Holland' study, a 14-year follow-up study of 1580 initially 4-16-year-olds who were drawn randomly from the Dutch general population. Because cannabis use is generally condoned in the Netherlands, false-negative reports of cannabis use may occur less frequently than in countries with stricter drug policies, which supports the value of the present study.


METHODS
Life-time cannabis use and psychotic symptoms, assessed with the Composite International Diagnostic Interview (CIDI).


RESULTS
Cannabis use, in individuals who did not have psychotic symptoms before they began using cannabis, predicted future psychotic symptoms (hazard ratio = 2.81; 95% confidence interval = 1.79-4.43). However, psychotic symptoms in those who had never used cannabis before the onset of psychotic symptoms also predicted future cannabis use (hazard ratio = 1.70; 95% confidence interval = 1.13-2.57).


CONCLUSIONS
The results imply either a common vulnerability with varying order of onset or a bi-directional causal relationship between cannabis use and psychosis. More research on patterns and timings of these relationships is needed to narrow down the possibilities.
Ferdinand
Robert F
RF
Department of Child and Adolescent Psychiatry, Erasmus Medical Center Rotterdam/Sophia Children's Hospital, Rotterdam, Netherlands. r.ferdinand@erasmusmc.nl
Sondeijker
Frouke
F
van der Ende
Jan
J
Selten
Jean-Paul
JP
Huizink
Anja
A
Verhulst
Frank C
FC
D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000523:psychology*; D009426:Netherlands; D011605:Psychoses, Substance-Induced / Q000209:etiology*; D011618:Psychotic Disorders / Q000150:complications*; D012307:Risk Factors