Medicare Part D Formulary: What Drugs Are Covered and How to Navigate Your Plan

When you enroll in Medicare Part D formulary, a list of prescription drugs covered by your Medicare drug plan. Also known as a drug list, it tells you exactly which medications your plan will pay for—and which ones won’t. This isn’t just a fine print document. It’s the key to knowing how much you’ll pay out of pocket for your pills each month.

Every Medicare Part D plan has its own formulary, and they’re not all the same. Some cover the same drugs but put them in different formulary tiers, categories that determine your cost-sharing. Tier 1 might be generic blood pressure pills costing $5, while Tier 4 could be specialty drugs like biologics costing $500. Your plan might cover Medicare Part D formulary drugs like lisinopril or metformin with low copays, but deny coverage for a similar drug just because it’s on a different tier. That’s why comparing plans isn’t just about premiums—it’s about what’s on the list.

Formularies change every year. A drug you got last year might suddenly need prior authorization, or get moved to a higher tier. That’s why you need to check your formulary every fall during Open Enrollment. If you take a drug for heart failure, diabetes, or COPD—like those mentioned in our posts on combination generics or triple inhaler therapy—you’ll want to confirm it’s still covered. Some plans require you to try cheaper options first (step therapy), or limit how much you can get at once (quantity limits). You might be surprised to find that your mail-order pharmacy savings only apply if your drug is on the formulary.

Doctors don’t always know your plan’s formulary. They might prescribe a brand-name drug because it’s what they’re used to, but your plan might only cover the generic version. That’s why asking, "Is this on my Part D formulary?" before you leave the office can save you hundreds. If your drug isn’t covered, you can request an exception. You’ll need your doctor to explain why it’s medically necessary, and many people get approved—especially if the alternatives caused side effects, like the GI issues with mycophenolate or the drowsiness from antihistamines.

Formularies also affect how you manage long-term conditions. If you’re on a drug like ibandronate for bone health or latanoprost for glaucoma, you need to know if it’s covered without restrictions. Same goes for blood pressure meds, where switching to a combination generic could cut your costs by 80%. Your formulary might even cover lab monitoring tools or injectable safety kits if they’re tied to your medication. The more you understand how your plan works, the less you’ll be stuck paying full price for something you thought was covered.

Below, you’ll find real-world guides on how generic drugs get approved, why prices vary between countries, how to save with mail-order pharmacies, and what to ask your doctor when your meds don’t work. These aren’t just theory—they’re tactics people use every day to make their Medicare Part D formulary work for them, not against them.