An individual who qualifies for either Medicare Part A or Medicare Part B will probably also qualify for a Prescription Drug Plan unless he or she has prescription drug coverage from an existing policy.  This allows seniors and others who qualify for Medicare to have much more comprehensive medical coverage since so many maladies are remediated by prescriptions.

Prescription Drug Plans come with varying levels of different benefits.  This allows one to tailor their coverage based on their needs and their budget.

Some Medicare Advantage policies include coverage for prescriptions.  None of the currently sold Medicare Supplement policies offer such coverage although some did in the past.  Policy holders who purchased those policies in the past are allowed to keep them, but new one cannot be sold today.

If you have prescription coverage from an existing health insurance policy, such as a Medicare Supplement or a Medicare Advantage policy, you will not qualify for a Prescription Drug Plan.  You may, however be able to drop the prescription benefits from your health policy coverage and apply for a PDP.