Medicare Advantage Part D (MAPD) plans must give at least a standard level of coverage set by Medicare.
Plans can vary the list of brand name prescription drugs and generic drugs they cover (called a formulary) and how they place drugs into different “tiers” on their formularies.
You can read more about prescription drug coverage in this Medicare publication: Your Guide to Prescription Drug Coverage
Formularies include at least two drugs in the most commonly prescribed categories and classes. The formulary might not include your specific drug but in most cases a similar drug is available. You can ask for an exception if you, or your prescriber, believe none of the drugs on your plan’s formulary will work for your condition.
A Medicare drug plan can change its drug list during the year as drug therapies change, new drugs are released, or new medical information becomes available if it follows guidelines set by Medicare.
Generic drugs must use the same active ingredients and work in the same way as the brand-name prescription drugs.
To keep costs low, many plans offer prescription drug coverage place drugs into different levels or “tiers” on their formularies. Each plan can divide its tiers in different ways and each tier costs a different amount. Usually, a drug in a lower tier will cost you less than a drug in a higher tier.