Understanding the effects of Medicare Part D from key stakeholders' perspectives: Important progress, but abundant research opportunities remain.

The Medicare Prescription Drug, Improvement, and Modernization Act of 2003 added prescription drug coverage to Medicare beginning in January 2006. The prescription drug coverage is voluntary, although beneficiaries face a significant penalty for delaying enrollment. The drug coverage is provided through private drug plans; beneficiaries have a choice of staying in the original Medicare program and receiving separate prescription drug coverage from a Medicare prescription drug plan (PDP) or receiving all their Medicare benefits though a private Medicare Advantage plan with prescription drug coverage (MA-PD). The Centers for Medicare and Medicaid Services (CMS) is responsible for administering this very complex program. Medicare Part D has dramatically reshaped the prescription drug insurance market and has had significant effects on insurers, beneficiaries, and providers. For researchers, it has provided a rich source of research questions to examine. This themed issue includes 7 articles in which researchers examine aspects of Medicare Part D from a variety of key stakeholder perspectives. One important outcome of Medicare Part D is its effects on prescription costs, addressed in this themed issue byMott et al and Goedken et al. By expanding access to prescription drug insurance, Medicare Part Dwas expected to increase prescription drug utilization and overall expenditures but decrease beneficiary out of pocket costs. Mott et al examined whether these effects differed by levels of pre-Part D drug spending. They concluded that Part D significantly reduced beneficiary out-of-