“Part D covers outpatient prescription drugs through private plans that contract with Medicare, including stand-alone prescription drug plans (PDPs) and Medicare Advantage plans with prescription drug coverage (MA-PDs). In 2019, beneficiaries have a choice of 27 PDPs and 21 MA-PDs, on average. The Part D benefit helps pay for enrollees’ drug costs and provides coverage for very high drug costs. Additional financial assistance is available for beneficiaries with low incomes and modest assets. Enrollees pay monthly premiums and cost sharing for prescriptions, with costs varying by plan. Enrollment in Part D is voluntary; in 2018, 43 million people on Medicare were enrolled in a PDP or MA-PD. Of this total, roughly one in four receive low-income subsides.”

Source: Issue Brief: An Overview of Medicare. Kaiser Family Foundation. February 2019. http://files.kff.org/attachment/issue-brief-an-overview-of-medicare