A formulary is a list of all the drugs covered by a health insurance plan. Health plans have different formularies, which means that a particular drug might be covered by one plan in your area, but not by another. Rebates from drug manufacturers to health plans’ pharmacy benefits managers can also affect which drugs end up on the formulary and into which drug tier they’re placed. However, the ACA imposed some minimum standards on all new individual and small-group plans in an effort to ensure that their formularies are robust and non-discriminatory: The formularies must include at least one drug in every United States Pharmacopeia (USP) category and class, OR the same number of drugs in each USP category and class as the state’s benchmark plan. And since 2017, the formulary creation process has been required to be guided by the recommendations of a pharmacy and therapeutics committee.