OBJECTIVES: To evaluate patterns of adjunctive therapy with anti-epileptic drugs (AED) and AED-specific pharmacy costs among patients with epilepsy over a six-year time period (2006-2011).   METHODS: Study patients were identified from the 2006-2011 PharMetrics Plus Database.  Separate patient cohorts were created for each year of analysis.  Patients ≥18 years of age with ≥2 claims for epilepsy (ICD-9-CM 345.XX) who were continuously eligible for the entire calendar year were selected.  Demographic characteristics, proportion of patients with adjunctive AED therapy (defined as a ≥ 60 day overlap in supply for two different AEDs) and AED pharmacy costs were evaluated for each calendar year.  Overall adjunctive AED therapy utilization was further stratified by AED generic/brand status using the following categories: adjunctive therapy with two generic AEDs, two branded AEDs, or one generic and one branded AED.  AEDs were identified and categorized based on NDC codes indicative of a generic/branded therapy for each year.   RESULTS: Patients meeting cohort selection criteria varied for each year of analysis, ranging from 28,013 to 61,444 (mean age 44.6-46.3 years).  The proportion of patients on adjunctive AED therapy stayed relatively constant over the analysis period, increasing only slightly over time (2006: 21.2%, 2007: 24.1%, 2008: 23.9%, 2009: 23.9%, 2010: 24.6%, 2011: 24.7%).   Adjunctive generic AED therapy utilization approximately doubled over the analysis period (2006: 11.5%, 2011: 21.7%), while branded therapy decreased 5-fold (2006: 3.1%, 2011: 0.6%) and generic/branded decreased by >50% (2006: 11.1%, 2011: 4.9%) adjunctive AED therapy decreased (all P<0.01).  Over the six-year analysis period, mean AED pharmacy costs among patients with epilepsy on any adjunctive AED therapy decreased by 7.6% (2006: $4,090, 2011: $3,778; P<0.01). CONCLUSIONS: In this study, a doubling in the utilization of generic drugs over a six-year period was associated with a 7.6% decrease in pharmacy cost.