The term substantial evidence, coined by the US Food and Drug Administration (FDA) as part of the Federal Food, Drug and Cosmetic Act, applies mostly to new drug development, but also to products that are already approved. Although it is practically applied to drugs, it is important for the personal care industry to understand its rationale, especially since cosmetic products are becoming more sophisticated. Moreover, the same approach might be used when a claim issue regarding a personal care product arises and the FDA must make a judgment.
When issuing warning letters to manufacturers that request substantial evidence, the FDA is asking for evidence to support all the advertising claims made, including but not limited to comparative claims. In reference to this term, the agency is not referring to the amount of evidence generated, nor to the quantity of persuasive, competent or reliable evidence. Instead, it is referring to the term in its technical sense, i.e., supportive data that will lead to a significant scientific agreement.1 The Federal Food, Drug and Cosmetic (FD&C) Act defines substantial evidence as “evidence consisting of adequate and well-controlled investigations, including clinical investigations, by experts qualified by scientific training and experience to evaluate the effectiveness of the drug involved, on the basis of which it could fairly and responsively be conducted by such experts ... .”