Sentence:  Even if beneficiaries want to stay in their current plan, they should still check that the drugs they take are remaining on their plan's <WSD>formulary</WSD> and on the same co-pay "tier" as before. 
Meaning of the word marked with <WSD> tags:  A list of drugs, created by health insurers, hospitals, or prescription drug plans, that defines how costs for any drug are shared between patient and health care provider, typically broken down by tiers such as preferred generics with lowest copay, or preferred brand with higher copay, or non-preferred brand and not covered tiers with the highest cost to the patient.