What Is a Formulary in Medicare Part D?

If you've ever heard the term "formulary" and thought it sounded complicated - it's not.

A formulary is simply a plan's list of covered prescription drugs.

But the details inside that list are where decisions are made.

What a Formulary Actually Does

Each Medicare Part D or Medicare Advantage plan with drug coverage has its own formulary.

That list determines:

Which drugs are covered
Which tier they fall into
What your cost-sharing may look like
Whether restrictions apply (prior authorization, step therapy, quantity limits)

No two formularies are identical.

What Most People Miss

The same medication can:

Be Tier 1 on one plan
Be Tier 3 on another
Require prior authorization on a third

And sometimes:

Brand vs generic placement changes the cost significantly
Dosage strength affects coverage tier
Pharmacy selection changes the amount you pay

That's why "I take three prescriptions" isn't enough information.

The details matter.

Drug Tiers in a Formulary

Most formularies organize drugs into tiers:

Tier	Typical Drug Type	Typical Cost
Tier 1	Preferred generics	Lowest
Tier 2	Non-preferred generics	Low
Tier 3	Preferred brand-name	Moderate
Tier 4	Non-preferred brand-name	Higher
Tier 5	Specialty drugs	Highest

Tier structures vary by plan - not all plans use the same number of tiers or the same drug assignments.

Formulary Restrictions

Beyond just covering a drug, formularies may include:

Prior Authorization: Plan approval required before coverage
Step Therapy: Must try a lower-cost drug first
Quantity Limits: Coverage restricted to certain amounts
Age Restrictions: Coverage limited by age criteria

These restrictions are listed in the formulary documents.

Why Formularies Change

Plans can update formularies annually.

Drugs may:

Move to a different tier
Be removed from the formulary
Add new restrictions
Gain preferred status

These changes are typically outlined in plan documents and the Annual Notice of Change.

Few people review them closely.

The Smarter Approach

Before enrolling - or during your annual review - verify:

Every medication by exact name
Dosage and frequency
Tier placement on the specific plan
Preferred pharmacy options
Any restrictions that apply

Drug coverage varies by plan and location.

Final Thought

A formulary isn't a minor detail.

It's a cost structure.

If you'd like to review how your medications are covered in plans available in your ZIP code (where permitted), we can walk through it calmly.

Clarity avoids surprises.

Benefits vary by plan, county, and eligibility. Always verify with the plan's Summary of Benefits before enrolling.

Frequently Asked Questions

A formulary is a Part D plan's list of covered prescription drugs. It defines which medications are covered, which tier each one sits in, what cost-sharing may look like, and whether restrictions like prior authorization or step therapy apply. Each plan builds its own formulary, so no two are identical.

Why is my drug covered on one plan but not another?

Each Medicare Part D and Medicare Advantage plan with drug coverage maintains its own formulary. A medication can be covered on one plan and excluded from another, or covered on both plans but at very different tier levels. That is why comparing formularies by exact drug name and dosage matters more than comparing premiums alone.

Can a plan remove a drug from its formulary mid-year?

Plans can update formularies during the year under specific circumstances, such as a generic becoming available or safety concerns. When that happens, plans typically have notification requirements and may offer transition supplies. Most major changes, however, take effect at the start of the new plan year and are described in the Annual Notice of Change.

What restrictions can a formulary place on a covered drug?

Common formulary restrictions include prior authorization (plan approval required before coverage), step therapy (you must try a lower-cost drug first), quantity limits (coverage capped at a certain amount per fill), and age-based criteria. A drug being on the formulary is not the full picture. . . the restrictions can affect whether and how you can fill it.

How do I check if my medications are covered before enrolling?

Pull together each medication by exact name, dosage, and frequency, then look up tier placement and any restrictions on the specific plan's formulary. Confirm preferred pharmacy options near you as well. A licensed agent can walk through the available plans in your ZIP code if you want a side-by-side comparison.