Medicare Part D
A Prescription Drug Plan (PDP) will have a premium, possibly a deductible, and tiered co-payments for covered medications. Each plan will have their own formulary, or list of covered drugs. No plan covers every drug, and every company organizes their formulary differently.
Medications are organized into tiers such as: preferred generic, non-preferred generic, preferred brand, non-preferred brand, and specialty. Some plans may have additional tiers, but this is the typical tier structure. Usually the lower the tier, the lower the co-pay.
Learn more about Medicare Part D here: Medicare Part D Overview