Drug tiers are definable by the plan. The option "tier" was introduced in the PBP to allow plans the ability to group different drug types together (i.e., Generic, Brand, Preferred Brand). In this regard, tiers could be used to describe drug groups that are based on classes of drugs. If the "tier" option is utilized, plans should provide further clarification on the drug type(s) covered under the tier in the PBP notes section(s). This option was designed to afford users additional flexibility in defining the prescription drug benefit.