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Using GLP-1s

Boxed warning

The FDA's most prominent drug-label warning, printed inside a black border at the top of the prescribing information. GLP-1 medications, injected and oral alike, carry one about thyroid C-cell tumors.

By the glp1.how editorial teamReviewed

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 GLP-1 medications carry a boxed warning about thyroid C-cell tumors, whether they are injected or taken as a pill. That covers semaglutide (including the Wegovy pill and Ozempic tablets), tirzepatide, liraglutide, dulaglutide, and orforglipron (Foundayo) (Wegovy (external link), Ozempic tablets (external link) and Foundayo (external link) prescribing information). The warning is based on rodent studies, not confirmed human cases. Orforglipron doesn't act on rodent GLP-1 receptors, so its label carries the warning because the human relevance of those rodent tumors hasn't been settled. In practice it means the drugs are not prescribed to people with a personal or family history of medullary thyroid carcinoma or MEN 2. The warning flags a specific risk your prescriber should screen for before you start. See the thyroid C-cell tumor warning: what it means and who it applies to.

boxed-warningfdasafetythyroid

Revision history

Updated 2 times since Sep 2, 2026 · show changes
  1. v3

    Body revised

  2. v2

    Summary rewritten; Body revised

  3. v1

    Change tracking began

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Related terms

  • Tirzepatide · A once-weekly dual GIP and GLP-1 receptor agonist made by Eli Lilly, marketed as Mounjaro for type 2 diabetes and Zepbound for weight management and obstructive sleep apnea.
  • 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.
  • 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.
  • 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.
  • Wegovy · Novo Nordisk's brand name for semaglutide (weekly injection or, since December 2025, a daily pill), FDA-approved for chronic weight management and heart-risk reduction, and as an injection for MASH liver disease.
  • Liraglutide · A first-generation GLP-1 receptor agonist taken as a daily injection, sold as Victoza for type 2 diabetes and Saxenda for weight management, and now also as a US generic.
  • Foundayo · Eli Lilly's brand name for oral orforglipron, a GLP-1 medication for adults with obesity or excess weight plus weight-related medical problems.
  • 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.

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