As a pharmacist, I read drug lists the way an accountant reads tax forms — and the single most expensive mistake I see people make during Medicare open enrollment is choosing a Part D plan without checking the formulary. The premium looks great, the copays look friendly, and then January arrives and their $12 refill is suddenly $85. This guide will show you how to read a Medicare Part D drug formulary the way a pharmacist does, so that never happens to you.
What a Formulary Actually Is
A formulary is simply a plan’s list of covered drugs. Every Part D plan has one, and every plan’s list is different. If your drug is not on the formulary, the plan won’t pay for it — so confirming your medications are covered before you enroll is the most important step in choosing a drug plan.
The 5-Tier Structure
Nearly every Part D plan organizes its formulary into five cost tiers. Lower tier, lower cost to you:
- Tier 1 — Preferred generics: the lowest-cost generics. Typical copay is just a few dollars.
- Tier 2 — Non-preferred generics: generics that cost a bit more, plus some low-cost brands.
- Tier 3 — Preferred brands: brand-name drugs the plan favors. Mid-range copays.
- Tier 4 — Non-preferred drugs: higher-cost brands and generics. Expect steeper copays.
- Tier 5 — Specialty drugs: high-cost medications for complex conditions. These often carry coinsurance (a percentage of the drug’s price) instead of a flat copay.
How to Search Your Plan’s Drug List
Every plan offers a formulary search tool on its website. Use it this way:
- Type in your drug’s exact name and dosage — a 20 mg tablet can sit on a different tier than a 40 mg tablet.
- Write down the tier number and the estimated copay or coinsurance for each of your medications.
- Check for restriction flags next to each drug — PA (prior authorization), ST (step therapy), or QL (quantity limits).
- Search for all of your medications, including ones you fill only occasionally.
Why the Same Drug Sits on Different Tiers Across Plans
This surprises people every year. Plans negotiate their own pricing with drug makers and pharmacies, so Drug X can be a $10 Tier 2 drug on one plan and a $47 Tier 3 drug on another. The drug is identical — the deal behind it isn’t. That is exactly why you can’t judge a plan by premium alone.
Prior Authorization, Step Therapy, and Quantity Limits
Three common restrictions you may see on a formulary:
- Prior authorization (PA): the plan must approve the drug before it covers it, usually requiring your doctor to explain why it is medically needed.
- Step therapy: the plan asks you to try a lower-cost drug first and only covers the pricier one if the first doesn’t work for you.
- Quantity limits (QL): the plan covers only a set amount per month — for example, 30 tablets per 30 days.
None of these are deal-breakers, but you want to know about them in October, not at the pharmacy counter in January.
My Pharmacist’s Tip: Check Every Fall
Plan details — tiers, copays, covered drugs, and restriction rules — can change year to year. A drug that was Tier 1 this year can move to Tier 3 next year. Never assume your plan looks the same as last year. Every fall, run your full medication list through your plan’s formulary tool before open enrollment ends. It takes ten minutes and can save you hundreds.
Need a Second Set of Eyes?
Reading formularies is literally what pharmacists do. If you’d like help comparing your medications against this year’s Part D plans, call me at (803) 415-7794 for a no-cost plan review. We’ll walk through your drug list together — no obligation, just clear answers.