Prescription Drugs
Formulary
Quick answer
A formulary is the official list of prescription drugs a Medicare Part D or Medicare Advantage plan covers, organized by tier. Every plan has its own formulary, and the same drug can be a different tier from one plan to another.
Plain-English definition
Drugs are grouped into tiers — usually preferred generics, generics, preferred brand, non-preferred brand, and specialty.
Why it matters
The best plan is almost always the one whose formulary treats your specific drugs best.
A simple example
Plan A places Eliquis on Tier 3; Plan B places it on Tier 2. Plan B saves you money even at a higher premium.
Common mistakes & misconceptions
- Comparing plans on premium alone.
- Assuming formularies never change — they can update each January.
Related terms
Drug Tier
Drug tiers group medications by cost. Lower tiers (preferred generics, generics) have the lowest copays; higher tiers (preferred brand, non-preferred brand, specialty) cost more.
Medicare Part D
Medicare Part D is prescription drug coverage sold by private insurance companies approved by Medicare. You get it either as a stand-alone drug plan (PDP) with Original Medicare or bundled inside most Medicare Advantage plans.
Tier Exception
A tier exception is a formal request for your plan to charge the lower-tier copay for a drug currently placed on a higher tier.
Preferred Pharmacy
A preferred pharmacy has a special contract with your Part D or Medicare Advantage plan that gives you lower copays on covered drugs compared to a standard network pharmacy.
Drug List
'Drug list' is the everyday name for a formulary — the list of prescription drugs a plan covers, organized by tier.
Frequently asked questions
Can a plan drop my drug mid-year?+
Plans can change formularies but must notify affected members.
Sources & references
📚 Where this information comes from
- Medicare.gov — official U.S. government site for people with Medicare ↗Primary source for benefits, enrollment periods, and plan comparison.
- CMS.gov — Centers for Medicare & Medicaid Services ↗Federal rulemaking, program updates, and official guidance.
- Social Security Administration — Medicare enrollment & premiums ↗Enrollment, premium withholding, and IRMAA determinations.
When you're ready, compare plans on your own terms
See Medicare Advantage plans from the insurance companies we represent, or walk the course with a licensed agent whenever you'd like a second set of eyes.
We help compare Medicare Advantage plans from the insurance companies we represent, and we don't offer every plan available in your area.
Medicare Caddies is an independent insurance agency. We are not affiliated with, endorsed by, or connected to the U.S. government, the federal Medicare program, or the Centers for Medicare & Medicaid Services (CMS). We help compare Medicare Advantage plans from the insurance companies we represent, and we don't offer every plan available in your area.