OBJECTIVES: Appropriate utilization of diabetes medications is key to improving clinical and financial effects of the disease. Pharmacy benefits may contain barriers to patients utilizing these medications. This study assessed the impact of elimination of member cost share and other benefit barriers on utilization of diabetes medications. METHODS: Study used a pre-post comparison of 1,281 individuals whose pharmacy benefits were provided by an employer that eliminated benefit barriers (member cost, refill restrictions, prior authorization) on 1/1/2006. Eligible study participants had continuous eligibility for pharmacy benefits from 1/1/2005 through 12/31/2006 and filled prescriptions for diabetes medication both before and after the benefit design change date. Adherence to therapy was measured by a weighted average of the therapeutic class Medication Possession Ratio (MPR) and was calculated during the period prior to the benefit change (1/1/2005 – 12/31/2005) and following it (1/1/2006 – 12/31/2006). RESULTS: Study population was 45% female (mean age 46.6). Subsequent to benefit design change, MPR increased by 2.0% (78.2% to 80.2%; p-value=0.003) for core diabetic therapy (insulin, sulfonylureas, metformin or combinations). Proportion of members with optimal adherence (80% or more MPR) increased from 58.6% to 64.9% (p-value <0.001). Average number of prescriptions per member did not change (11.7 vs. 11.7; p-value=0.95), but days supply increased significantly (362 days vs. 459 days; p-value <0.001) with no detectable increase in mail utilization. Proportion of members using adjunct therapy (glucosidase inhibitors, amylin & GLP-1 analogs) in addition to core therapy increased significantly from 4.6% to 10.2% (p-value <0.001), primarily due to increased use of Byetta®. CONCLUSION: Removal of pharmacy benefit barriers improves an individual's ability to achieve optimal adherence to diabetes medication and thereby achieve clinical goals. In conditions such as diabetes where optimal therapy adherence has significant implications, one should consider decreasing or removing member cost share and other benefit barriers.