Background:
Cannabis is the most widely used illicit drug in Australia with higher rates of use found among those with a mental disorder. The similarities of the effects of cannabis to symptoms of psychosis, particularly schizophrenia, and the observation that cannabis use is temporally linked to the development of schizophrenia symptoms in some people, have led to a plethora of research investigating the relationship between cannabis use and psychosis. Contrary to hypotheses, recent research investigating cannabis use among an ‘ultrahigh-risk’-for-psychosis sample found that cannabis use or dependence in the year prior to recruitment to the study was not associated with a heightened risk of developing psychosis over the following 12-month period. The current research was a similar, cross-sectional retrospective study of cannabis use among an ultrahigh-risk group, conducted at the Psychological Assistance Service, Newcastle, New South Wales, from June 2004.
Aims:
The study aimed to investigate 1) the lifetime patters of cannabis use among an ultrahigh-risk sample; 2) the relationship between cannabis use and risk factors, symptoms and other psychosocial outcomes and 3) the relationship between cannabis use and/or other clinical markers and subsequent transition to psychosis.
Results:
Over 75% of the sample had tried cannabis at service entry and high rates of cannabis use were comparable with other early psychosis cohorts. Earlier cannabis use initiation was associated with increased cannabis use. There was poorer psychosocial functioning in the no-use group and high-use group. High cannabis use alone was not associated with transition to psychosis among the ultrahigh-risk sample; however, findings were in the expected direction. High cannabis use at service entry in combination with family history of psychosis or brief limited psychotic symptoms was associated with significantly greater risk of transition to psychosis.
Conclusions:
Cannabis use needs to be addressed in the ultrahigh-risk population. The contribution that cannabis makes to transition to psychosis among an ultrahigh-risk group may be difficult to identify, that is, the proportion of increased risk that cannabis use contributes to developing psychosis may require population studies or larger ultrahigh-risk samples. The neurodevelopmental ‘cannabinoid hypothesis’ and the ‘two-hit’ hypothesis of schizophrenia may help guide future research into composite risk factors for psychosis, for example, family history and high cannabis use.
