Key Takeaways
- Each Part D and Medicare Advantage drug plan has its own formulary.
- Drugs are grouped into cost tiers.
- Formularies can change from year to year.
A formulary is the list of prescription medications a drug plan agrees to cover, usually organized into tiers that determine your cost. A lower tier means a smaller copay.
Because formularies change annually, a plan that covered your medications affordably last year may not this year — one reason an annual review pays off.