Medicare Part D was established in 2006 to cover the costs of prescription medications. The costs of prescriptions started to rise above a level of affordability for many U.S. residents. The primary function of Part D is to mitigate those costs and make certain people are capable of receiving the medicine needed to stay healthy. 

Medicare Part D plans are also sold by third-party, private insurance companies on the open market. It is a good strategy to compare the plans across several companies to find those offering coverage for medications you already take routinely. The healthcare marketplace allows you to compare up to four plans at once, making it easier to compare features.

As with Medicare Advantage all companies are required to follow federally mandated rules and regulations.

Certain Medicare enrollees receive prescription medications free or at low costs. 

If you have a disability, are low income or have an end stage disorder, then many of your prescription costs may be low to no cost.

Those falling into these categories receive special forms to fill out, or you may obtain them from your healthcare provider. The healthcare marketplace also asks you a series of questions to determine your eligibility to have your end stage prescription costs covered. 

Premiums for Part D vary per provider, as do copays and other out-of-pocket expenses. Similar to Medicare Part B, Part D carries a late enrollment penalty if members choose to not enroll in it when initially eligible.

Finally, enrollees are charged twenty-five percent of their total prescription medication costs after their initial, cumulative prescription costs reach $4,020 each year.