A product's legal identity under federal law is decided not by what is in the bottle but by what the seller says it does. This article explains the intended use doctrine that turns a lotion into a drug and a supplement into an unapproved new drug, and works through the categories the Food, Drug, and Cosmetic Act creates. It covers the dietary supplement framework created by DSHEA including the structure-function claim safe harbor, the disclaimer, new dietary ingredient notification, and the drug exclusion provision that keeps CBD out of the supplement category. It then covers the health claim tiers and the First Amendment litigation in Pearson v. Shalala that produced qualified health claims, the cosmetic rules as changed by MoCRA in 2022, and the FTC's separate and stricter advertising substantiation regime after POM Wonderful. Later sections cover the device pathways and their very different preemption consequences, drug labeling preemption from Wyeth v. Levine through Bartlett, off-label promotion after Caronia and Amarin, and the enforcement ladder that ends with individual criminal liability under the responsible corporate officer doctrine.