Impact of Cannabis and Other Drugs on Age at Onset of Psychosis

Ana González-Pinto, Ph.D., M.D.; Patricia Vega, Ps.; Berta Ibáñez, Ph.D., M.Sc.; Fernando Mosquera, M.D.; Sara Barbeito, Ps.; Miguel Gutiérrez, Ph.D., M.D.; Sonia Ruiz de Azúa, Ph.D., Ps.; Iván Ruiz, M.D.; and Eduard Vieta, Ph.D., M.D.

Objective: The aim of this study was to investigate the relationship between age and cannabis use in patients with a first psychotic episode, and to analyze the mediating effect of comorbid use of other drugs and sex on age at onset of psychosis.

Method: All consenting patients (aged 15 to 65 years) with a first psychotic episode needing inpatient psychiatric treatment during a 2-year period between February 1997 and January 1999 were considered, confirming a total of 131 patients. Subjects were interviewed using the Structured Clinical Interview for DSM-IV Axis I Disorders, and clinical and demographic data were collected. We used general linear models with age at onset as the response variable and survival Cox models to confirm the results. Both a multivariate linear model and the corresponding Cox model were fitted with a covariate that summarizes the most significant contributors that seemed to decrease age at onset.

Results: Regarding the effect of cannabis use, a significant gradual reduction on age at onset was found as dependence on cannabis increased, consisting in a decrement of 7, 8.5, and 12 years for users, abusers, and dependents, respectively, with respect to nonusers (p = .004, p < .001, and p < .001, respectively). 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. The finding was similar in the youngest patients, suggesting that this effect was not due to chance.

Conclusion: The major contribution of this investigation is the independent and strong link between cannabis use and early age at onset of psychosis, and the slight or nonexistent effect of sex and comorbid substance abuse in this variable. These results point to cannabis as a dangerous drug in young people at risk of developing psychosis.

(J Clin Psychiatry 2008;69:1210-1216. Online Ahead of Print July 29, 2008.)

Received Oct. 18, 2007; accepted Jan. 15, 2008. From the Department of Psychiatry, Santiago Apóstol Hospital, CIBER-SAM, Vitoria, Spain (Drs. González-Pinto, Mosquera, Gutiérrez, Ruiz de Azúa, and Ruiz and Mss. Vega and Barbeito); Basque Foundation for Health Innovation and Research (BIOEF), Sondika, Spain (Dr. Ibáñez); Hospital Clinic, University of Barcelona, IDIBAPS, CIBER-SAM, Barcelona, Spain; and International Consortium for Bipolar Disorders Research, Harvard Medical School and McLean Division of Massachusetts General Hospital, Boston, Mass. (Dr. Vieta).

This research was supported by Health Research Funds from the Spanish Government (FIS: PI05/2761, PI06/1416, RD06/0011/0014, FI05/00763, Red de Enfermedades Mentales REM-TAP Network RD-06), by European Regional Development Funds (FEDER), and by the Health Department of the Basque Government (2004/11016, 2006/111025) and Caja Vital 2006 and 2007. The research psychiatric department in Santiago Apóstol Hospital (03-RC-003) and the Barcelona Bipolar Disorders Program are supported by the Stanley Medical Research Institute.

Dr. González-Pinto has been awarded by a Specific collaborative agreement between the Spanish Government (SCIII) and Basque Government to stabilize and intensify research in the National Health System (B.O.E. no. 21; January 24, 2007). Dr. Vieta is a consultant to AstraZeneca, Bristol Myers Squibb, Eli Lilly, GlaxoSmithKline, Janssen, Lundbeck, Sanofi, Servier, Novartis, Organon, Otsuka, and Pfizer; has received grant/research support from AstraZeneca, Bristol Myers Squibb, Eli Lilly, GlaxoSmithKline, Janssen, Novartis, Otsuka, Pfizer, Sanofi, and Servier; and is a member of the speakers/advisory boards for AstraZeneca, Bristol Myers Squibb, Eli Lilly, GlaxoSmithKline, Janssen, Novartis, Organon, Otsuka, Pfizer, Sanofi, and Servier. Mss. Vega and Barbeito and Drs. Ibáñez, Mosquera, Gutiérrez, Ruiz de Azúa, and Ruiz report no additional financial or other relationships relevant to the subject of this article.

Corresponding author and reprints: Ana González-Pinto, Ph.D., M.D., Department of Psychiatry, Santiago Apóstol Hospital, CIBER-SAM, Vitoria, Álava 01004, Olaguibel, 29; 8th Floor, Sector B, Spain

(e-mail: ANAMARIA.GONZALEZ-PINTOARRILLAGA@osakidetza.net).