A drug formulary is a list of medications covered by your insurance, organized into tiers based on factors like cost and effectiveness. Lower-tier drugs (e.g., generics) cost less, while higher-tier drugs (e.g., brand-name or specialty medications) can be more expensive and may require prior authorization. Formularies change over time, and drugs may be added or removed, which can affect coverage and costs. If a needed drug isn’t on your formulary, you can request a “formulary exception” through your doctor, which has a pretty good chance of being approved.