An Examination of the Influence of Cannabis Use on Psychotic Symptom Exacerbation and Relapse in Early Psychosis

Abstract

There has been concern about the impact of cannabis use on the onset, course and relapse of psychosis. Evidence from retrospective and a small number of prospective studies has suggested that cannabis use may precipitate a latent psychosis, exacerbate psychotic symptoms and increase the likelihood of psychotic relapse. The purpose of the current study was to examine the influence of cannabis use on psychotic symptom exacerbation and relapse within the stress vulnerability-coping model of psychosis. Two studies were conducted. The influence of cannabis use on the onset and course of psychosis was retrospectively examined in the first study. The second study prospectively examined the influence of cannabis use on psychotic symptom exacerbation and relapse over a 6-month period. The influence of the severity of psychotic symptoms on a relapse in cannabis use was also explored. Eighty-four participants were assessed at admission, 81 of whom were followed up for a 6-month period. Measures consisted of structured diagnostic interviews and self-report measures of stress, medication compliance, family functioning, premorbid adjustment, quality of life, substance use and psychotic symptoms. The onset of cannabis use clearly preceded the onset of psychosis. Cannabis use was predictive of the severity of psychotic and general psychopathology symptoms at admission. Both the frequency and quantity of cannabis use was predictive of time to psychotic relapse over the 6-month follow up period. Psychotic symptom severity was predictive of a substantial increase in the quantity but not the frequency of cannabis use. Cannabis use was related to the onset, course and relapse of psychosis.