Every Part D plan has something called a formulary, which is a list of drugs covered under the plan. Each formulary has a set of tiers, and in most cases, Part D plans have between three and six tiers. A lower-tier drug usually has lower copays or coinsurance than a drug in a higher tier.

For example:

• Tier 1 – Lowest copay, usually generic drugs
• Tier 2 – Medium copay includes some low-cost brand-name drugs
• Tier 3 – Higher copay includes brand-name drugs that have generic versions also available
• Tier 4 – Higher-co-pay brand-name drugs, and some specialty drugs
• Tier 5 – Highest copay includes high-cost specialty prescription drugs

Suppose you are prescribed a drug in a high tier, and a drug that is similar or therapeutically equivalent is also available in a lower-tier at a lower price. In that case, you can ask your insurance company for an exception to get the lower coinsurance or copay.