Treatment adherence with lithium and anticonvulsant medications among patients with bipolar disorder.

OBJECTIVE: Nonadherence limits the effectiveness of medications among patients with bipolar disorder. This study examined adherence with lithium and anticonvulsant medication among patients with bipolar disorder receiving treatment in Department of Veterans Affairs (VA) settings.
METHODS: Patients receiving treatment in the VA for bipolar disorder during federal fiscal year 2003 (FY03) and receiving lithium or anticonvulsant medication were identified (N=44,637) by using the VA's National Psychosis Registry. Medication adherence was assessed by using the medication possession ratio (MPR) for lithium, valproate or divalproex, carbamazepine, and lamotrigine. Patients were categorized into three groups: fully adherent (MPR greater than .80), partially adherent (MPR from more than .50 to .80), and nonadherent (MPR less than or equal to .50).
RESULTS: A slight majority of individuals (54.1%) were fully adherent, 24.5% were partially adherent, and 21.4% were nonadherent. Nonadherent individuals were more likely to be younger, unmarried, nonwhite, or homeless or to have diagnoses of a substance use disorder or fewer outpatient psychiatric visits in FY03. Adherence intensity was somewhat lower for valproate, compared with lithium or other anticonvulsants. Individuals given prescriptions for two agents to stabilize mood had better adherence than individuals given prescriptions for a single agent. Unexpectedly, in multivariate analyses adjusting for prior hospitalization, number of outpatient psychiatric visits, and a diagnosis of substance use disorder, poorer adherence was associated with decreased rates of hospitalization.
CONCLUSIONS: Nearly one in two individuals given prescriptions for lithium or anticonvulsant medication to treat bipolar disorder did not take their medications as prescribed. The effectiveness of bipolar medication treatments is reduced by high rates of nonadherence in clinical settings.