To explore the relationship between cannabis use and self-report dimensions of psychosis in a population of university students presenting for any reason to primary care.

One thousand and forty-nine students attending the Student Health Unit, National University of Ireland, Galway, completed self-report questionnaires on alcohol and substance misuse, non-clinical dimensions of psychosis (Community Assessmemnt of Psychic Experiences), anxiety and depression (Hospital Anxiety and Depression Scale). Association of cannabis use with psychiatric symptoms was explored whilst controlling for confounds.

More frequent cannabis use was independently associated with greater intensity of positive, negative and depressive psychotic symptoms. The earlier the age of onset of cannabis use, the more positive psychotic symptoms were reported.

These findings support the hypothesis that cannabis use increases the risk of developing psychotic symptoms and that this risk is further increased in those individuals who use cannabis more heavily and commence it at a younger age.