Drug Formularies & Tier Structure
Medicare Part D plans organize prescription drug coverage through defined formularies and tier structures. These elements determine which medications are covered and how cost-sharing is applied. Understanding how formularies and tiers operate provides clarity on how prescription costs are calculated under Part D.
What Is a Formulary?
A formulary is the official list of prescription medications covered by a specific Part D plan. Each plan maintains its own formulary, subject to Medicare approval. Covered medications and formulary placement may vary between plans.
Drug Tiers and Cost-Sharing
Part D formularies typically organize medications into tiers. Each tier corresponds to a level of cost-sharing defined by the plan’s design. Lower tiers often include generic medications, while higher tiers may include brand-name or specialty drugs. The impact of tier placement is explained further in Coverage Phases & Cost Structure.
Tier Placement and Exceptions
Drug tier placement is determined by the plan and may affect copayment or coinsurance amounts. In certain circumstances, individuals may request a formulary exception if a prescribed medication is not covered or is placed in a higher tier, subject to plan rules and medical justification.
Annual Formulary Changes
Formularies may change from year to year. Medications may move between tiers, require additional authorization, or be removed from coverage. Reviewing prescription coverage during the Annual Enrollment Period helps ensure continued alignment with medication needs.
Disclaimer: This information is provided for educational purposes only and is based on publicly available guidance from the Centers for Medicare & Medicaid Services (CMS). It has not been reviewed or endorsed by Medicare, CMS, or any federal agency. This content does not constitute plan-specific advice. For individual coverage questions, please consult a licensed insurance professional.