OBJECTIVES: A key goal for managed care organizations is to improve patient health outcomes and reduce costs. One strategy involves increasing medication adherence among patients with chronic diseases. The Kentucky Department for Medicaid Services contracted with three managed care organizations in November 2011 to transition the state’s traditional fee-for-service Medicaid patients into capitated managed care. The purpose of this study is to determine differences in medication adherence before and after the switch from fee-for-service to managed care for Medicaid patients in Kentucky with essential hypertension between 2010 and 2012. METHODS: The retrospective cohort study sample will be drawn from a database of Kentucky Medicaid patient (age 18-64) medical and prescription claims between 2010 and 2012. The University of Kentucky Internal Review Board approved the study. The study will include descriptive statistics of the medication possession ratio (MPR) and control variables including patient demographics, type of antihypertensive, and comorbidities. Bivariate analyses will measure the effect of each variable on the change in MPR as a result of the switch. Multivariate analysis will be a difference-in-difference regression model, measuring the pre and post differences in MPR due to the introduction of managed care. RESULTS: Initial data collected indicate that average MPR decreased by about 13 percentage points, regardless of medication class, after Medicaid managed care in Kentucky took effect, with other factors held constant. A 13-percentage point decrease in MPR corresponds to about 45 fewer days of medication possession. CONCLUSIONS: Results are preliminary, but indicate a need to address the efficacy of Medicaid managed care on adherence to antihypertensives in Kentucky. Additional studies should be conducted with data from 2013 to ensure confounding due to transitional issues is eliminated. Future studies will examine the effect of Medicaid managed care on adherence in hyperlipidemia, diabetes, asthma, and mental health disorders.