Medical foods are a distinct FDA regulatory category different from single molecule chemical pharmaceuticals, and from dietary supplements. The FDA has regulated amino acid preparations as drugs since the 1940s as they can elicit pharmacologic effects similar to conventional single molecule pharmaceuticals. The best known amino acid preparations are used to treat conditions such as maple syrup disease and phenylketonuria (PKU). An official definition and categorization of medical foods was made in 1988 as part of the Orphan Drug Act. Medical foods are regulated similarly to drugs except they do not require pre-approval because all ingredients are found on the FDA's generally recognized as safe (GRAS) (Sections 201(s) and 409 of the Federal Food, Drug, and Cosmetic Act) list and claims are confined to the nutritional management of a specific disease. Medical food claims must be supported by recognized scientific data as determined by medical evaluation. A GRAS substance is distinguished from a food additive on the basis of the common knowledge about the safety of the substance for its intended use. The standard for an ingredient to achieve GRAS status requires not only technical demonstration of non-toxicity and safety, but also general recognition of safety through widespread usage and agreement of that safety by experts in the field. Many ingredients have been determined by the FDA to be GRAS, and are listed as such by regulation, in Volume 21 Code of Federal Regulations (CFR) Sections 182, 184, and 186.