boxed warning

Every prescription drug sold in the United States carries a label, a long technical document written for prescribers rather than patients. Most of its warnings sit in the body of that document. A small number are pulled to the very front and printed inside a black box, and those are boxed warnings.

The rule is written into US federal regulation. Under 21 CFR 201.57, certain contraindications or serious warnings, particularly those that may lead to death or serious injury, may be required by the FDA to be presented in a box. The heading has to carry the word WARNING in capitals and say what the warning is about, and the box has to explain the risk briefly and point to the fuller section of the label that covers it. A summary of it must also appear in the highlights on the label's first page, capped at twenty lines.

A boxed warning is not the same as a ban, and it does not mean the harm is common. It means the regulator judged the risk serious enough that a prescriber should not be able to miss it. Drugs in wide everyday use carry them, and reading one tells you what the FDA thinks is worth stopping to weigh before writing the prescription.