Amends part D (Voluntary Prescription Drug Benefit Program) of title XVIII (Medicare) of the Social Security Act to direct any prescription drug plan that has in its network one or more pharmacies located in a health professional shortage area, in a medically underserved area, or among a medically underserved population, and that provides a reduction in coinsurance or copayments for covered part D drugs, to extend to any pharmacy located in that area, or among that population, the option to be an in-network pharmacy under terms and conditions comparable to those the plan has agreed upon with other in-network pharmacies located in the area or among that population.