The FDA regulates dietary supplements as foods, and not as drugs. The FDA does not pre-approve dietary supplements on their safety and efficacy, unlike drugs. In contrast, the FDA can only go after dietary supplement manufacturers after they have put unsafe products on the market. However, certain foods (such as infant formula and medical foods) are deemed special nutritionals because they are consumed by highly vulnerable populations and are thus regulated more strictly than the majority of dietary supplements.

The claims that a dietary supplement makes are essential to its classification. If a dietary supplement claims in any way to cure, mitigate, or treat a disease, it would be considered to be a unauthorized new drug and in violation of the applicable regulations and statutes. As the FDA states it:

No, a product sold as a dietary supplement and promoted on its label or in labeling as a treatment, prevention or cure for a specific disease or condition would be considered an unapproved--and thus illegal--drug. To maintain the product's status as a dietary supplement, the label and labeling must be consistent with the provisions in the Dietary Supplement Health and Education Act (DSHEA) of 1994.

The only claims that a dietary supplement is allowed to make are structure/function claims. These are broad claims that the product can support the structure or function of the body (e.g., "glucosamine helps support healthy joints"). The FDA must be notified of these claims within 30 days of their first use, and there is a requirement that these claims be substantiated. Nevertheless, many critics claim that dietary supplements overstate their importance and their impact on overall health. Evidence of their benefits has yet to meet standard scientific criteria of credibility, based on large scale, double blind testing with statistically significant outcomes.