While Original Medicare covers only hospital and medical insurance, you can purchase a separate Part D prescription drug plan. Part D plans cover at least two drugs in each therapeutic category and cover essentially all drugs in six categories: anticancer, anticonvulsant, antidepressant, antipsychotic, antiretroviral, and immunosuppressant.

Each plan lists its covered drugs in a formulary. If one of the prescriptions you take is not on your plan’s formulary and cannot be substituted with a covered drug, you and your prescriber can request an exception. You can also request an exception if you need your medication in a higher quantity than the limit allows.

Qualified plans can remove brand-name drugs from their formularies and replace them with generic drugs, or change the price of the brand-name drug when they add generic options. Plans can also make changes to their drug lists throughout the year if drug therapies change, new drugs enter the market, new medical information becomes available, a drug becomes unavailable, or the Food and Drug Administration (FDA) considers a drug to be unsafe.

When a plan changes to covered prescriptions, it is required to notify you and keep you supplied with medication. If a change affects a drug you are currently taking, you will be given at least 30 days’ advance notice or provided at least a month’s supply of medication.