Objective: This naturalistic study used claims data to examine the relationship of medication nonadherence to hospital use and costs among severely mentally ill clients in Wisconsin. Methods: Data for 619 clients were obtained from Medicaid drug and hospital claims, county records, and case managers as part of a larger study in eight county-based mental health systems. Study participants were eligible for Medicaid, had a severe and persistent mental illness, were 18 years or older, and were receiving neuroleptics, lithium, or antidepressants. Drug claims were analyzed for a 12-month period to determine how regularly clients obtained their medications. Regression analyses were used to assess the effects of irregular medication use on any hospitalization for psychiatric problems, the number of days hospitalized, and hospital costs. The analyses controlled for several risk factors. Results: Among clients with schizophrenia or schizoaffective disorder, 31 percent used medications irregularly. The rates were 33 percent among those with bipolar disorder and 41 percent among those with other severe mental illnesses. In the total sample, irregular users had significantly higher rates of hospitalization than regular users (42 percent versus 20 percent), more hospital days (16 days versus four days), and higher hospital costs ($3,992 versus $1,048). Irregular medication use was one of the strongest predictors Of hospital use and costs even after the analyses controlled for diagnosis, demographic characteristics, baseline functioning, and previous hospitalizations. Conclusions: The availability of drug claims data and the ability to use them in predictive analyses make them a potentially useful data source in studies of medication adherence among persons with severe mental illness.
