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Using GLP-1s

Medullary thyroid carcinoma (MTC)

A rare thyroid cancer arising from the thyroid's C cells; a personal or family history of it is a contraindication to GLP-1 medications.

By the glp1.how editorial teamReviewed

Medullary thyroid carcinoma (MTC) is a rare form of thyroid cancer that arises from the thyroid's C cells. It is the reason GLP-1 medication labels carry a boxed warning, based on findings that some of these drugs caused thyroid C-cell tumors in rodents; whether the same risk applies to humans has not been established.

A personal or family history of MTC, or of the inherited syndrome MEN 2, is listed as a contraindication to GLP-1 receptor agonists. For what the warning does and doesn't mean in practice, see our guide on the thyroid C-cell tumor warning on GLP-1 medications.

The Ozempic label's boxed warning says semaglutide causes thyroid C-cell tumors in rodents, that the human relevance hasn't been determined, and that it's contraindicated with a personal or family history of MTC or MEN 2 (Ozempic prescribing information (external link)).

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Revision history

Updated 1 time since Sep 2, 2026 · show changes
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    Body revised

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Related terms

  • Boxed warning · The FDA's strongest prescription-drug warning, set in a black-bordered box at the top of the label to flag a serious or life-threatening risk.
  • GLP-1 · A gut hormone (glucagon-like peptide-1) that stimulates insulin release, slows digestion, and reduces appetite; the target of drugs like semaglutide and liraglutide.
  • MEN 2 (multiple endocrine neoplasia type 2) · An inherited syndrome that raises the risk of medullary thyroid carcinoma and is a contraindication to most GLP-1 medications.
  • Semaglutide · A GLP-1 receptor agonist medication made by Novo Nordisk, sold under the brand names Ozempic (type 2 diabetes) and Wegovy (weight management), each as an injection or a pill.
  • Ozempic · Novo Nordisk's brand name for semaglutide for type 2 diabetes, sold as a weekly injection and, since May 2026 in the US, as daily Ozempic tablets.

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