Total population-based study of the impact of substance use disorders on the overall survival of psychiatric inpatients.

Background: Patients with severe mental illness have a shortened lifespan, and substance use disorder (SUD) is an especially important diagnosis in this respect. There have been no studies comparing directly SUD to other diagnoses in a nationwide cohort.

Aims: To directly compare differences in mortality rates of psychiatric inpatients with a discharge diagnosis of SUD versus other psychiatric diagnoses.

Methods: A register-based study was made of all patients admitted to psychiatric hospitals in Iceland between 1983 and 2007. Patients were grouped according to discharge diagnoses. Survival with respect to SUD was compared using Cox-proportional hazard ratio, excluding those with an organic mental disorder. Furthermore, the survival of patients with SUD and co-morbid diagnoses was evaluated.

Results: A total of 14,281 patients (over the age of 18 years) were admitted to a psychiatric hospital in Iceland during the study period, with a total of 156,356 years of follow-up. For both men and women, a diagnosis of SUD conferred similar mortality as a diagnosis of schizophrenia without SUD, while individuals with a diagnosis of a mood disorder or "other disorders" had significantly lower mortality than SUD. For men with SUD, a co-occurring mental disorder was associated with an increased risk of dying, however, this was not found for women.

Conclusions: SUD was the psychiatric diagnosis that had the highest mortality rate among psychiatric inpatients, in both men and women. An additional psychiatric diagnosis on a pre-existing SUD diagnosis did increase the risk for men but not women.