Part D plans are not required to pay for all covered Part D drugs. They establish their own formularies, or list of covered drugs for which they will make payment, as long as the formulary and benefit structure are not found by CMS to discourage enrollment by certain Medicare beneficiaries. Part D plans that follow the formulary classes and categories established by the United States Pharmacopoeia will pass the first discrimination test. Plans can change the drugs on their formulary during the course of the year with 60 days' notice to affected parties.