Substance use: a powerful predictor of relapse in schizophrenia

This study examined substance use among a group of 37 schizophrenia patients participating in a year-long fluphenazine decanoate (FD; Prolixin) dosage reduction study (Inderbitzin et al. (1994) Am. J. Psychiatry 151, 1753-1759). Ten (50%) of the 20 FD dose-reduced patients, and 6 (35%) of the 17 control group patients were identified as substance users. The dose-reduced and control groups did not differ significantly in substance use. We examine here the 37 patients regrouped by substance users (n = 16) versus non-users (n = 21) to determine the effects of substance use. In addition to identifying substance users and types of substances used, we hypothesize that substance users differ demographically from non-users, have worse symptomatology, worse compliance, higher rates of relapse, and therefore, can confound studies. Clinical and demographic data were obtained. At least half of the substance users were using alcohol or cocaine. The substance use group had a significantly higher severity of illness score on the BPRS at study onset. We found no significant differences between the two groups on other rating scales. The non-use group lived more independently, and the substance use group was younger. The substance use group had nearly twice as many hospitalizations in the 2 years prior to the study, a greater rate of missed appointments in the year before and during the study, and 4 times as many relapses during the year of the study than the non-use group. The key finding was that among 9 of the 37 patients who relapsed in the year of the study, 7 of the 9 had a history of substance use. Substance use was found to be a better predictor of relapse and hospitalization than gradual 50% dosage reduction of FD in the related study. Substance use among schizophrenia patients is a major complicating factor.