Association between age at onset of psychosis and age at onset of cannabis use in non-affective psychosis.
BACKGROUND
Several studies have associated cannabis use with the development of schizophrenia. However, it has been difficult to disentangle the effects of cannabis from that of other illicit drugs, as previous studies have not evaluated pure cannabis users. To test whether the onset of cannabis use had an effect on the initiation of psychosis, we examined the time relationship between onset of use and onset of psychosis, restricting our analysis to a cohort of individuals who only used cannabis and no other street drugs.


METHODS
Fifty-seven subjects with non-affective psychoses who used cannabis prior to developing a psychosis were interviewed using the Diagnostic Interview for Genetic Studies (DIGS). The Family Interview for Genetic Studies (FIGS) was also used to interview a family informant about psychiatric illness in the patient and the entire family. Multiple linear regression techniques were used to estimate the association between variables.


RESULTS
After adjusting for potential confounding factors such as sex, age, lifetime diagnosis of alcohol abuse or dependence, and family history of schizophrenia, the age at onset of cannabis was significantly associated with age at onset of psychosis (β=0.4, 95% CI=0.1-0.7, p=0.004) and age at first hospitalization (β=0.4, 95% CI=0.1-0.8, p=0.008). The mean time between beginning to use cannabis and onset of psychosis was 7.0±4.3. Age at onset of alcohol use was not associated with age at onset of psychosis or age at first hospitalization.


CONCLUSIONS
Age at onset of cannabis is directly associated with age at onset of psychosis and age at first hospitalization. These associations remain significant after adjusting for potential confounding factors and are consistent with the hypothesis that cannabis could cause or precipitate the onset of psychosis after a prolonged period of time.
VA Boston Healthcare System. 940 Belmont Street, Brockton, MA 02301, USA. Juan_Galvez-Buccollini@hms.harvard.edu
Juan A
JA
Galvez-Buccollini
Ashley C
AC
Proal
Veronica
V
Tomaselli
Melissa
M
Trachtenberg
Cristinel
C
Coconcea
Jinsoo
J
Chun
Theo
T
Manschreck
Jerry
J
Fleming
Lynn E
LE
Delisi
D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000437:Alcoholism; D016009:Chi-Square Distribution; D005260:Female; D006760:Hospitalization; D006801:Humans; D007406:Interview, Psychological; D008297:Male; D002189:Marijuana Abuse / Q000175:diagnosis / Q000453:epidemiology* / Q000235:genetics; D011569:Psychiatric Status Rating Scales; D011618:Psychotic Disorders / Q000175:diagnosis* / Q000453:epidemiology* / Q000235:genetics; D012307:Risk Factors; D055815:Young Adult