The impact of substance use disorders on the course of schizophrenia--a 15-year follow-up study: dual diagnosis over 15 years.

BACKGROUND: This follow-up study compared patients with schizophrenia with co-occurring substance use disorder to patients with schizophrenia and no substance use disorder. AIMS: To investigate the prognostic significance of the effects of substance use disorders on the course of schizophrenia.
METHOD: Patients with schizophrenia and co-occurring substance use disorder (n=107), and patients with schizophrenia only (n=119) were followed over a 15-year period through the use of national hospitalization registers, data for time and cause of death, and data for homelessness or institutionalization.
RESULTS: The median length of psychiatric hospitalization was 12 days for a patient with dual diagnosis, and 21 days for patients with schizophrenia only. Patients with dual diagnosis displayed a significantly elevated usage of all types of hospital contacts except inpatient treatment for non-psychiatric disorders. In three types of hospital contacts, patients with co-occurring substance use had approximately two to three times as many hospitalizations as did patients with schizophrenia only. Rates for homelessness and institutionalization were similar in both groups. Patients with a dual diagnosis were also significantly more at risk of dying during follow-up than were patients with schizophrenia only.
CONCLUSIONS: The findings suggest that the long-term course of schizophrenia is considerably more severe in patients who have a dual diagnosis compared to patients with schizophrenia only Substance use disorders have a substantial impact on the hospitalization rates of patients with schizophrenia, as well as on life expectancy. Patients with co-morbid substance abuse are more likely to be admitted for treatment during a given year although they have briefer contact with treatment.