Prescription Drug Guide
Formularies, tiers, and how to pick a Part D plan.
How Part D works
Private insurers offer stand-alone Part D plans that add drug coverage to Original Medicare. Medicare Advantage plans usually bundle Part D. Each plan has its own monthly premium, deductible, and copay structure.
Formularies — check yours
Every plan publishes a formulary, a list of the specific drugs it covers. Before picking a plan, run your exact medications through the plan's formulary. A plan can be cheap on paper and still cost you thousands if it doesn't cover your prescriptions or puts them on a high tier.
Tiers explained
Formularies are grouped into tiers. Tier 1 (preferred generics) is cheapest; Tier 5 (specialty drugs) is most expensive. If a drug you take is on a high tier, ask your doctor whether a lower-tier alternative would work.
The coverage phases
You typically go through a deductible phase, an initial coverage phase (with copays), and — under recent changes — a yearly out-of-pocket maximum that caps what you pay for covered drugs each year. The old "donut hole" no longer works the way it once did.
Extra Help (Low-Income Subsidy)
If your income and resources are limited, Extra Help can dramatically lower Part D premiums, deductibles, and copays. Apply through Social Security — there is no fee. Qualifying automatically opens a Special Enrollment Period to change plans.
Compare every year
Plans change formularies, tiers, and pricing every January. During AEP (Oct 15 – Dec 7), re-run your medications through Medicare's Plan Finder. The plan that was best last year often isn't best next year.