Your Medicare Plan Might Not Cover Your Prescriptions the Way You Think

You picked your Medicare plan. You thought your medications were covered. Then you walked up to the pharmacy counter and the number on the receipt stopped you cold.

This happens more than it should. And it's almost always preventable.

What Part D Actually Is

Medicare Part D is prescription drug coverage. It's not built into original Medicare — it's a separate plan you add on, sold through private insurance companies.

If you're on a Medicare Supplement plan, you'll add a standalone Part D plan. If you're on Medicare Advantage, drug coverage is usually bundled in — but the specific drugs covered and what you pay for them vary widely from plan to plan.

Every Part D plan has something called a formulary — a list of the specific drugs the plan covers. Not every drug is on every formulary. And even when your drug is covered, what you pay depends on which tier it falls on.

How Formulary Tiers Work

Think of tiers like levels. Most Part D plans have five tiers, and the higher the tier, the more you pay out of pocket.

Tier 1 — Preferred generic drugs. Usually $0–$5 per prescription.

Tier 2 — Non-preferred generics. Usually $10–$20.

Tier 3 — Preferred brand-name drugs. Usually $30–$50.

Tier 4 — Non-preferred brand-name drugs. Can run $80–$100 or more.

Tier 5 — Specialty drugs. These can cost hundreds of dollars per fill, sometimes more.

Here's the problem. Many people are on brand-name medications — for blood pressure, diabetes, heart conditions — that land on Tier 3, 4, or even 5. If you're on three or four of those, your monthly drug costs can easily exceed what you budgeted.

And formularies change every year. A drug on Tier 2 this year may be on Tier 4 next year.

The Coverage Gap — What the Donut Hole Is

You may have heard the term "donut hole." It refers to a coverage gap that kicks in after you and your plan have spent a certain amount on covered drugs in a calendar year.

Once you hit the initial coverage limit — currently around $5,030 in total drug costs — you enter the coverage gap. In the gap, you pay a larger share of your drug costs until you reach a catastrophic coverage threshold.

The rules around the donut hole have improved significantly over the years, and in 2025 a new $2,000 out-of-pocket cap on Part D costs takes effect, which is a meaningful change. But the coverage gap still exists in modified form, and understanding how it affects your specific medications is important — especially if you take expensive drugs regularly.

The Mistake People Make at Enrollment

Most people choose a Medicare plan based on the premium. That's understandable — the monthly cost is the most visible number.

But the premium is only part of the story. A plan with a $0 premium and a bad formulary for your specific medications can cost you far more than a plan with a $40 premium and good formulary coverage.

The only way to know what you'll actually pay is to run your specific medications through each plan's drug search tool before you enroll. Every Medicare plan is required to provide a searchable formulary. You enter your drugs, and it shows you what tier they're on and what you'd pay.

It takes about 20 minutes. Most people skip it entirely.

How to Check Your Drugs Before You Enroll

Here's exactly what to do before picking any Medicare plan that includes drug coverage:

Make a list of every medication you take. Include the name, dosage, and how often you fill it.

Go to Medicare.gov's Plan Finder tool — or work with an independent agent who will do this for you. Enter your drugs and compare what each plan would cost you for those specific medications over the full year.

Look at total annual cost, not just premium. Add up your premiums plus your estimated drug costs for the year. That's your real number.

Do this again every fall during Open Enrollment. Formularies change. Your costs can shift significantly from one year to the next even if your medications don't change.

A Simple Step That Most People Skip

Checking your formulary before you enroll is one of the highest-value things you can do in the entire Medicare process. It takes a little time. It requires knowing your medications. And it can save you hundreds — sometimes thousands — of dollars a year.

Nobody warns you about this clearly enough at enrollment time. Now you know.

Key Takeaways

• Every Part D plan has a formulary — a list of covered drugs assigned to cost tiers. Higher tiers mean higher copays.

• Always check your specific medications against a plan's formulary before you enroll — never assume they're covered

• Formularies change every year, making an annual review essential for anyone who takes regular prescriptions

Drug coverage is one of the most overlooked parts of Medicare planning — and one of the most expensive to get wrong. If you'd like help running your medications through the available plans in your area, that's exactly what we do. Reach out and we'll take a look together.