Psychological Medicine

Original Articles

Cannabis use at a young age is associated with psychotic experiences

C. D. Schubarta1 c1, W. A. van Gastela1, E. J. Breetvelta1, S. L. Beetza1, R. A. Ophoffa1a2a3, I. E. C. Sommera1, R. S. Kahna1 and M. P. M. Boksa1a4

a1 Rudolf Magnus Institute of Neuroscience, University Medical Centre Utrecht, Department of Psychiatry, The Netherlands

a2 UCLA Center for Neurobehavioral Genetics, Los Angeles, CA, USA

a3 Department of Medical Genetics, University Medical Centre Utrecht, The Netherlands

a4 Julius Center for Health Sciences and Primary Care, University Medical Centre Utrecht, The Netherlands


Background Cannabis use is associated with psychosis and a range of subclinical psychiatric symptoms. The strength of this association depends on dosage and age at first use. The current study investigates whether level of cannabis exposure and starting age are associated with specific profiles of subclinical symptoms.

Method We collected cross-sectional data from a young adult population sample by administering an online version of the Community Assessment of Psychic Experiences (CAPE). Cannabis exposure was quantified as the amount of Euros spent on cannabis per week and the age of initial cannabis use. The primary outcome measure was the odds ratio (OR) to belong to the highest 10% of scores on the total CAPE and the positive-, negative- and depressive symptom dimensions.

Results In 17 698 adolescents (mean age 21.6, s.d.=4.2 years), cannabis use at age 12 years or younger was strongly associated with a top 10% score on psychotic experiences [OR 3.1, 95% confidence interval (CI) 2.1–4.3] and to a lesser degree with negative symptoms (OR 1.7, 95% CI 1.1–2.5). The OR of heavy users (>€25/week) for negative symptoms was 3.4 (95% CI 2.9–4.1), for psychotic experiences 3.0 (95% CI 2.4–3.6), and for depressive symptoms 2.8 (95% CI 2.3–3.3).

Conclusions Early start of cannabis use is strongly associated with subclinical psychotic symptoms and to a lesser degree with negative symptoms, while smoking high amounts of cannabis is associated with increased levels of all three symptom dimensions: psychotic, negative and depressive. These results support the hypothesis that the impact of cannabis use is age specific.

(Received April 27 2010)

(Revised August 19 2010)

(Accepted August 24 2010)

(Online publication October 07 2010)


c1 Address for correspondence: C. D. Schubart, M.D., University Medical Centre Utrecht, HP. B.01.206, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. (Email: