Impact of Medicare Part D on Cancer and Diabetes Disparities among Dual Enrollees Despite the availability of effective therapies to treat chronic disease, disparities in the use of these medicines persist. Racial and ethnic minorities are disproportionately represented among the more than 7 million dual Medicaid and Medicare enrollees, who were transitioned from Medicaid to Medicare Part D drug coverage plans on January 1, 2006. Concerns have been raised about the random assignment of dual enrollees to Part D plans, due to varying benefits and reported declines in coverage. Few studies have examined the impact of coverage policy on disparities in medication use and related health outcomes. The implementation of Medicare Part D offers a unique opportunity to investigate the consequences of a major change in national coverage policy on health disparities. Our application focuses on two principal mechanisms by which Medicare Part D may impact health disparities among dual enrollees: 1) the removal of limits on the number of reimbursable prescriptions per month and 2) randomization of enrollees to plans with varying availability of medications for chronic disease management. The removal of prescription drug limits in some states may reduce gaps in medication use and, for high risk subgroups, access-related disparities in outcomes. For dual enrollees in all states, the ability to navigate Part D related changes in benefits (i.e., medication accessibility) may be mediated through patient (e.g., English language proficiency, education, usual source of care) and care setting characteristics that interact with race and ethnicity. Taking advantage of the random assignment of dual enrollees to Part D plans, we will use a strong quasi-experimental and an experimental design to investigate the impact of Medicare Part D drug coverage on racial and ethnic disparities among dual enrollees overall and among high risk chronically ill subgroups. Because of variation in Medicaid and in Part D plan benefits, each state represents a separate natural policy experiment. The goal of this study is to move beyond the documentation of health disparities to understanding the impact of coverage policy on disparities and potential mediating factors. PUBLIC HEALTH RELEVANCE: Impact of Medicare Part D on Cancer and Diabetes Disparities among Dual Enrollees Access to appropriate health care services is a key driver of differences in health services use and outcomes by race and ethnicity. However, few studies have evaluated the impact of changes in public insurance programs (e.g., Medicaid, Medicare) on health disparities. The purpose of this study is to investigate the impact of a major change in national health insurance coverage (the passage of Medicare Part D) on disparities in health services use, outcomes and costs among vulnerable chronically ill patients.