A boxed warning (often called a "black box warning") is the strongest safety notice the FDA can require on a prescription drug's label. It appears inside a black border at the very top of the prescribing information and is reserved for risks that are serious, potentially life-threatening, or that need to be weighed carefully against a drug's benefits.
The injectable GLP-1 medications — semaglutide, tirzepatide, liraglutide, and dulaglutide — all carry a boxed warning about thyroid C-cell tumors. It is based on rodent studies rather than confirmed human cases, and in practice it means the drugs are not prescribed to people with a personal or family history of medullary thyroid carcinoma or MEN 2. A boxed warning doesn't mean a drug is unsafe for most people; it means there is a specific risk your prescriber should screen for. See the thyroid C-cell tumor warning: what it means and who it applies to.