Black box warning

When does FDA require a boxed warning?

A black box warning is a warning that FDA may require to be presented in a box on a drug's label. Federal regulation names "certain contraindications or serious warnings, particularly those that may lead to death or serious injury" [1]. The warning ordinarily rests on clinical data, but serious animal toxicity can be the basis instead when clinical data doesn't yet exist [1]. The box carries an uppercase heading containing the word "WARNING" and briefly explains the risk, then points to the label's Contraindications or Warnings and Precautions sections for detail [1]. The regulation's name for it is a boxed warning [1].

Why do GLP-1 labels carry one?

Wegovy and Zepbound each carry a boxed warning for thyroid C-cell tumors. In animal studies, semaglutide caused these tumors in rodents and tirzepatide caused them in rats; the labels state that whether the finding applies to humans "has not been determined" [2][3]. The same box states that the drugs are contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2 [2][3].

Does a boxed warning mean the drug isn't approved?

No. Wegovy and Zepbound are FDA-approved and carry boxed warnings on their approved labels [2][3]. Regulation requires the box to briefly explain the risk and then point readers to the label's Contraindications or Warnings and Precautions sections for the complete picture [1]. It is one flagged risk inside a longer label, not a separate document.