Drugs on a formulary are often organized into different drug “tiers”. Your cost depends on which drug tier your drug is in. For example, a plan may form tiers this way: Tier 1 – Generic drugs. Tier 2 – Preferred brand-name drugs. Tier 3- Non-preferred brand name drugs. Contact the plan to learn more about its specific tier structure.

References

https://www.medicare.gov/find-a-plan/staticpages/glossary/planfinder-glossary.aspx