Background: Substance abuse worsens the course of schizophrenia, but it is not known whether or not there are differences between specific substances concerning their association with the hospitalizations of patients with schizophrenia.
Aims: The primary aims of this study were to examine the possible associations between amphetamine, cannabis, and opioid abuse, and the risk of hospitalizations among patients with schizophrenia.
Methods: The study population consisted of 146 patients with ICD-defined schizophrenia from two different geographical sites in Finland, and it included both inpatients and outpatients. Data were collected retrospectively from the patients' medical files. Substance abuse was defined as either harmful use or dependence according to ICD-10.
Results: The cumulative prevalence of substance abuse was 10.9% (16/146) for cannabis, 8.9% (13/146) for amphetamine, and 4.1% (6/146) for opioids. Among patients with schizophrenia and abuse of any substance, the number of hospitalizations was about 1.5-fold when compared to those without substance abuse. The incidence rate ratio for hospitalizations was 2.9 (95% CI 2.47-3.63) for opioids, 2.0 (1.71-2.41) for amphetamine, and 1.6 (1.33-1.84) for cannabis, when compared with no abuse of each substance. The risk of hospitalizations was significantly higher for opioids when compared with amphetamine (p < 0.001) or cannabis (p < 0.001).
Conclusions: Harmful use or dependence of opioids among patients with schizophrenia is associated with significantly higher risk of hospitalizations than either harmful use or dependence of amphetamine or cannabis.
Keywords: Amphetamine; Cannabis; Hospitalization; Opioid; Schizophrenia.