Psychological Medicine

Original Articles

Acute cannabis use causes increased psychotomimetic experiences in individuals prone to psychosis

O. Masona1, C. J. A. Morgana1, S. K. Dhimana1, A. Patela1, N. Partia1, A. Patela1 and H. V. Currana1 c1

a1 Clinical Psychopharmacology Unit, University College London, London, UK


Background Epidemiological evidence suggests a link between cannabis use and psychosis. A variety of factors have been proposed to mediate an individual's vulnerability to the harmful effects of the drug, one of which is their psychosis proneness. We hypothesized that highly psychosis-prone individuals would report more marked psychotic experiences under the acute influence of cannabis.

Method A group of cannabis users (n=140) completed the Psychotomimetic States Inventory (PSI) once while acutely intoxicated and again when free of cannabis. A control group (n=144) completed the PSI on two parallel test days. All participants also completed a drug history and the Schizotypal Personality Questionnaire (SPQ). Highly psychosis-prone individuals from both groups were then compared with individuals scoring low on psychosis proneness by taking those in each group scoring above and below the upper and lower quartiles using norms for the SPQ.

Results Smoking cannabis in a naturalistic setting reliably induced marked increases in psychotomimetic symptoms. Consistent with predictions, highly psychosis-prone individuals experienced enhanced psychotomimetic states following acute cannabis use.

Conclusions These findings suggest that an individual's response to acute cannabis and their psychosis-proneness scores are related and both may be markers of vulnerability to the harmful effects of this drug.

(Received April 10 2008)

(Revised October 06 2008)

(Accepted October 06 2008)

(Online publication November 19 2008)


c1 Address for correspondence: Professor H. V. Curran, Clinical Psychopharmacology Unit, Clinical Health Psychology, University College London, Gower Street, London WC1E 6BT, UK. (Email: