NEW YORK (Reuters Health) – Researchers from Spain have found a strong and independent link between cannabis use and early age at onset of psychosis. The association, they say, cannot be explained by chance, is dose related, and independent of gender and comorbid use of other drugs.

“The clinical importance of this finding is potentially high,” Dr. Ana Gonzalez-Pinto from Santiago Apostol Hospital in Vitoria, and colleagues write in the Journal of Clinical Psychiatry for August, given that cannabis use is extremely prevalent among young people.

According to the researchers, “estimates of the attributable risk suggest that the use of cannabis accounts for about 10% of cases of psychosis.”

The findings are based on 131 patients aged 15 to 65 years needing inpatient care for a first psychotic episode during a 2-year period. Subjects were interviewed using the Structured Clinical Interview for DSM-IV Axis I Disorders, and clinical and demographic data were collected.

The results showed a significant gradual reduction in age at psychosis onset as dependence on cannabis increased. Compared with nonusers, age at onset was reduced by 7, 8.5, and 12 years, respectively, in cannabis users, abusers and dependents, they report.

“Multivariate analysis showed a clear effect of cannabis use on age at onset, which was not explained by the use of other drugs or by gender,” they also note. The finding was similar in the youngest patients, suggesting that this effect was not due to chance.”

These results “point to cannabis as a dangerous drug in young people at risk of developing psychosis,” Dr. Gonzalez-Pinto and colleagues conclude.

Reference:
J Clin Psychiatry 2008;69:1210-1216.