Part D Formulary: What’s Covered, What’s Not, and How to Save on Medications

When you enroll in Medicare Part D, a federal program that helps pay for prescription drugs for people on Medicare. Also known as Medicare prescription drug coverage, it’s not one single plan—it’s a network of private insurance plans that each create their own list of covered drugs, called a Part D formulary, a list of medications approved for coverage under a specific Medicare drug plan. This list determines what you can get, how much you pay, and whether you need prior authorization to fill a prescription.

Every Part D formulary is split into tiers, categories that group drugs by cost and preference. Tier 1 usually includes generic drugs with the lowest copay. Tier 2 is for preferred brand-name drugs. Tier 3 is for non-preferred brands, and Tier 4 or 5 often includes high-cost specialty drugs. Some plans even have a tier for drugs that require special approval before they’re covered. If your medication is on a higher tier, you could pay hundreds more per month—even if it’s the exact same drug your doctor prescribed. That’s why checking your plan’s formulary before you enroll matters. A drug you take daily might be covered under Tier 1 with a $5 copay in one plan, but Tier 4 with a $120 copay in another. And if your drug isn’t on the formulary at all, you’ll pay full price unless you file an exception request.

Formularies change every year. Plans can remove drugs, move them to higher tiers, or add new restrictions like step therapy—where you have to try a cheaper drug first before they’ll cover the one your doctor picked. That’s why you can’t just pick a plan once and forget it. Every fall, during Open Enrollment, you need to review your current plan’s formulary against your meds. If your cholesterol drug got bumped to Tier 5, or your antidepressant was dropped entirely, you might need to switch plans before January 1.

Not all drugs are covered. Part D plans don’t cover drugs for weight loss, fertility, or cosmetic use. Some also exclude over-the-counter meds, even if your doctor recommends them. And if you’re taking something like Tricor for triglycerides or Victoza for diabetes, make sure it’s listed—not just because it’s expensive, but because if it’s not on the formulary, your out-of-pocket cost could be double what you expect.

What you’ll find in the posts below are real-world guides on how to navigate these rules. You’ll learn how to read your formulary like a pro, how to challenge a denial, how to find cheaper alternatives that are still covered, and how to avoid getting stuck with a bill for a drug your plan suddenly stopped paying for. Whether you’re managing high blood pressure, diabetes, depression, or chronic pain, understanding your Part D formulary isn’t just paperwork—it’s how you keep your meds affordable and your health on track.