Short answer: Both. But – once eligible for Medicare, Part D is the primary payor for dual eligibles for prescription medication and Medicaid is always the insurer of last resort. To complicate matters, Medicaid covers certain medications not covered by Part D, such as benzodiazepines, barbiturates, medications for eating disorders, certain OTC medications not covered by Part D, and some prescription vitamins.
Further, one must be enrolled in a Medicare prescription drug plan to continue receiving Medicaid benefits, except under very limited circumstances. Enrollment is automatic, but the beneficiary may switch to a different Part D plan at any time and still retain Medicaid as secondary coverage.
Medicaid provides a “wrap-around” benefit for medications such as: antidepressants, atypical antipsychotics, antiretrovirals used in the treatment of HIV/AIDS, and immunosuppressants used in the treatment of tissue and organ transplants. However, benefits must first be denied by Part D. Despite the existence of the wrap-around benefit, beneficiaries are expected to appeal to their insurance program and/or Part D to obtain alternative coverage for those medications which Medicaid covers at the time claims are denied by other insurers. “Prescribers are expected to continue to work with their patient’s Medicare Part D plans utilizing the exception and appeal process in order to obtain coverage for necessary medications.” More information is available at http://www.health.ny.gov/health_care/medicaid/program/medicaid_transition/faq.htm.
To ensure continuity of care and in an attempt to simplify obtaining benefits, the Affordable Care Act established a Medicare-Medicaid Coordination Office for dual eligibles. More information about this is available at www.cms.gov/medicare-medicaid-coordination/.
Information about public health insurance eligibility screening is here.