Food and Drug Administration (FDA) has issued two draft interim guidance documents that address the use of bulk drug substances in compounding under Sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act (FD&C Act). Under Section 503A of the FD&C Act, compounders can only use bulk substances that are included in the United States Pharmacopeia, the National Formulary monograph, or if it is on a list promulgated as a regulation pursuant to Section 503A(b)(1)(A)(i)(III) of the FD&C Act. Under Section 503B of the FD&C Act, bulk substances can only be used in compounding if they are used to compound a drug that is on FDA’s drug shortage list at the time of compounding, distribution, and dispensing or on FDA’s 503B bulk list. According to the documents, drug substances that are nominated after (or on the date of) the finalized date cannot be used until FDA has reviewed the nomination to determine if the substance has sufficient supporting information to be included on the bulk list.