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14-12-2010 | Mental health | Article

Cannabis use linked to sub-clinical psychotic symptoms in students


Free abstract

MedWire News: Cannabis use is associated with the occurrence of sub-clinical psychotic symptoms in a dose-dependent manner among university students presenting to primary care for any reason, study results show.

"Our findings contribute to the existing body of work linking cannabis use to the expression of psychosis and add strength to the suggestion that younger cannabis users are at greatest risk," Louise Conlon (National University of Ireland, Galway, Ireland) and colleagues comment in the journal Acta Psychiatrica Scandinavica.

Community studies have indicated that psychotic symptoms are relatively common in non-clinical populations, supporting the concept of a continuum of psychosis, from clinical psychotic disorders through to normality.

Notably, some studies have reported a relationship between cannabis use and dimensions of psychosis in non-clinical populations.

Given that cannabis use has been reported to be widespread among university populations in several European countries and in the USA, it would be interesting to address psychotic tendencies in such a population, Conlon et al note.

To investigate, they assessed 1049 students attending the Student Health Unit at the National University of Ireland using self-report questionnaires on alcohol and substance misuse, non-clinical dimensions of psychosis (Community Assessment of Psychic Experiences (CAPE).

In all, 423 (40%) students reported ever using cannabis with 327 participants reporting light use (1-30 occasions of lifetime use) and 86 reporting heavy use of the drug (30+ occasions of lifetime use).

There was a significant effect of frequency of cannabis use on positive symptom score, whereby those in the heavy-use group had more symptoms than those in the light-use group or those in the never-use group, with average scores of 1.35, 1.24 and 1.22, respectively. There was no significant difference between those in the light-use and never-use groups.

Similarly, there was a significant effect of frequency of cannabis use on negative symptom score, whereby those in the heavy-use group and those in the light-use had more symptoms than those in the never-use group, with average scores of 1.65, 1.53, and 1.50, respectively. In this instance, there was no significant difference between the heavy-use group and the light-use groups.

Furthermore, there was an age-dependent trend whereby those students who reported earlier age at first use of cannabis also reported more positive psychotic symptoms.

The researchers say that the dose-dependent and age of first use effects seen in the study provide strong evidence that cannabis directly contributes to psychotic symptoms.

Nevertheless, they cannot categorically rule out "reverse causality" whereby individuals might medicate for existing underlying psychotic symptoms.

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Andrew Czyzewski

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