When you hear “PFAS,” you probably think of nonstick cookware, waterproof jackets, or contaminated drinking water. You probably don’t think of the prescription sitting in your medicine cabinet. Yet fluorinated compounds classified as per- and polyfluoroalkyl substances (PFAS) are built into a surprisingly wide range of approved pharmaceuticals, often not because they’re essential to how those medicines treat disease, but because they make the drug easier to formulate.