Wegovy and Zepbound carry a boxed warning, the FDA’s most prominent label warning, about the risk of thyroid C-cell tumors, and the Foundayo label contraindicates the same patient groups. The Wegovy label says semaglutide caused thyroid C-cell tumors in rodents in a dose- and treatment-duration-dependent way; the Zepbound label says it is unknown whether tirzepatide causes such tumors, including medullary thyroid carcinoma (MTC), in humans. All three labels say not to use the medicine if you or a family member has had MTC, or if you have multiple endocrine neoplasia syndrome type 2 (MEN 2). A large 2025 cohort study in people with type 2 diabetes found no increased thyroid cancer risk versus another diabetes drug class over a median follow-up of 1.8 to 3.0 years, but its authors said that was too short to rule out risk with long-term use. Tell your prescriber about any thyroid or family cancer history before you start.
If you are considering a GLP-1 medicine, the thyroid warning is probably the first safety statement you will see, and it is easy to misread. It is written in the language of animal studies and rare cancers, which can sound alarming or, once people learn the human evidence is reassuring so far, dismissive. This article walks through what the current FDA labels for Wegovy, Zepbound and Foundayo actually say, what medullary thyroid cancer is, what the largest recent human study found, and what questions to bring to your prescriber. It does not tell you whether a medicine is right for you. Only a clinician who knows your history can do that.
What the boxed warning says, label by label
A boxed warning is the FDA’s strongest label warning for a medicine’s risks. Each label below was checked on 7 October 2026 against the manufacturer-hosted prescribing information.
The Wegovy label (revised 06/2026) states in its boxed warning that in rodents, semaglutide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors. It says Wegovy is contraindicated in patients with a personal or family history of MTC, and it instructs prescribers to counsel patients about the potential risk of MTC. Section 4 (Contraindications) lists a personal or family history of MTC, or MEN 2. Section 5.1 describes the mouse and rat findings and tells clinicians to inform patients of symptoms of thyroid tumors, such as a mass in the neck, trouble swallowing, trouble breathing or persistent hoarseness.
The Zepbound label (revised 08/2026) has a boxed warning with a more cautious wording about humans: it says it is unknown whether Zepbound causes thyroid C-cell tumors, including MTC, in humans. Section 5.1 reports that in rats, tirzepatide caused a dose-dependent and treatment-duration-dependent increase in the incidence of thyroid C-cell tumors. The label contraindicates use in patients with a personal or family history of MTC or with MEN 2, and tells prescribers to counsel patients on the potential risk and on the symptoms listed above.
The Foundayo label (orforglipron tablets, revised 07/2026) contraindicates use in patients with a personal or family history of MTC or with MEN 2 (section 4), and its patient-counseling section (section 17) says to inform patients that in rodent studies, medicines that work like Foundayo caused thyroid C-cell tumors, and to report symptoms such as a lump in the neck or persistent hoarseness. The label as retrieved also carries a boxed warning on this risk that tells prescribers to counsel patients about the potential risk of MTC.
In plain terms, the three labels agree on the practical instructions even where the animal-study language differs: do not use the medicine if you have the contraindicating history, know the symptoms, and report them.
Who should not take these medicines because of the thyroid warning
The contraindication has two parts, and both come straight from section 4 of each label.
- A personal or family history of medullary thyroid carcinoma. “Family history” matters because some MTC is inherited. If a parent, sibling or child has had MTC, tell your prescriber even if you have never had a thyroid problem yourself.
- Multiple endocrine neoplasia syndrome type 2 (MEN 2). This is an inherited condition that raises the chance of MTC and other endocrine tumors.
The labels do not list other thyroid conditions, such as an underactive thyroid, thyroid nodules or the common papillary thyroid cancers, as contraindications in the sections we reviewed. That does not mean they are irrelevant to your decision, only that the contraindication is specific to MTC and MEN 2. If you have a thyroid history of any kind, your prescriber should know about it. For a wider picture of who is told to avoid these medicines, see who should not take an oral GLP-1.
What medullary thyroid cancer is, and why it is the focus
The thyroid contains two main cell types. Follicular cells make thyroid hormone. C cells, also called parafollicular cells, make a hormone called calcitonin. The rodent findings on the labels concern C-cell tumors, which is why the human concern is MTC, the cancer that arises from C cells.
According to the American Thyroid Association, MTC accounts for 1% to 2% of thyroid cancers in the United States. It can run in families: the ATA says inherited forms account for up to 25% of diagnoses, linked to MEN 2A and MEN 2B, while in the majority of patients (about 75%) no germline mutation is found and the cases are called sporadic. MTC usually presents as a lump or nodule in the thyroid, though it may cause no symptoms, and the ATA notes that thyroid function tests such as TSH are usually normal even when MTC is present. Advanced disease can cause neck, jaw or ear pain, breathing or swallowing problems, and hoarseness.
That last point explains a line in the labels that surprises many readers. Wegovy section 5.1 and Zepbound section 5.1 both say that routine monitoring of serum calcitonin or using thyroid ultrasound is of uncertain value for early detection of MTC. In other words, the labels do not ask your prescriber to screen you with these tests while you are on treatment. Instead they rely on the contraindication before you start and on symptom awareness afterward. Calcitonin is used in other settings: the ATA describes it as a tumor marker used to confirm an MTC diagnosis and to follow patients after treatment. Those are different uses from screening healthy people.
Rodent findings versus human evidence
Why do rodents matter? Regulators ask for animal carcinogenicity studies, and in rodents this class of medicine produced C-cell tumors in a dose-dependent and treatment-duration-dependent pattern, which is what the Wegovy and Zepbound labels report. But the label language on humans is cautious, not conclusive. Zepbound’s boxed warning says it is unknown whether the medicine causes these tumors in humans, and nothing in the labels says that human cases have been shown to be caused by the medicine.
Human studies have tried to fill the gap. A 2025 international multisite cohort study in the journal Thyroid (Baxter and colleagues) used six population-based databases from Canada (Ontario), Denmark, Norway, South Korea, Sweden and Taiwan. It identified 98,147 GLP-1 receptor agonist users and 2,488,303 users of DPP-4 inhibitors, another diabetes drug class, among people with type 2 diabetes. GLP-1 use was not associated with an increased risk of thyroid cancer (pooled weighted hazard ratio 0.81, 95% confidence interval 0.59 to 1.12), and the authors saw no increased risk with higher cumulative dose. They could not analyze thyroid cancer subtypes, which means the study cannot speak directly to MTC. The follow-up was short, with a median of 1.8 to 3.0 years among GLP-1 users, and the authors wrote that the evidence was insufficient to rule out excess risk with long-term use.
Two cautions apply when you read a result like this. First, the population was people with type 2 diabetes, not necessarily people taking these medicines for weight management, and medicines were compared against a different drug class rather than against no treatment. Second, a hazard ratio whose confidence interval spans 1 means the study did not detect a difference; it does not prove no difference exists. The honest summary is that the best recent human data are reassuring over the short to medium term and silent on the very long term. That is also why the labels keep the boxed warning in place.
Symptoms to report, and who to tell
The labels give a specific list for patients to report to a clinician: a lump or mass in the neck, difficulty swallowing, difficulty breathing, and persistent hoarseness. Several of these overlap with far more common and benign problems, such as a cold, reflux or a benign thyroid nodule, so having one does not mean you have a tumor. What the labels ask is that the symptom be reported rather than ignored, particularly if it persists. Do not stop a prescribed medicine on your own because of a symptom. Contact your prescriber, who can examine you and decide what testing, if any, is appropriate.
Because the thyroid warning matters most before you start, the intake step is where you can act. When you complete a health questionnaire for any prescriber, in person or through a telehealth service (see our online GLP-1 telehealth reviews), check how the form asks about thyroid cancer, MEN 2 and family history, and answer accurately. If you do not know your family history, ask relatives before the appointment if you can. Questions worth asking include whether anyone in your family has had thyroid cancer, and whether any relatives have had adrenal or parathyroid tumors, which are linked to MEN 2 syndromes.
How this differs from other label warnings
The thyroid warning is a boxed warning and a contraindication. Other warnings in the same labels, such as pancreatitis and gallbladder disease, are in the Warnings and Precautions section and do not by themselves bar use. The distinction affects how you plan: a contraindication is an up-front screening question, while a precaution is something to monitor and discuss. Several other topics sit between the two, including pregnancy planning and surgery or anesthesia.
Common misunderstandings
- “The boxed warning means it causes thyroid cancer in people.” The Wegovy label describes findings in rodents, and Zepbound’s boxed warning says it is unknown whether the medicine causes these tumors in humans.
- “A recent study proves it is safe.” The 2025 cohort study found no increased overall thyroid cancer risk over a median of 1.8 to 3.0 years, but its authors said it could not rule out risk with long-term use and could not analyze subtypes.
- “Any thyroid condition rules the medicine out.” The contraindication named in the labels is a personal or family history of MTC, or MEN 2. Other thyroid history still deserves a conversation.
- “I should get a calcitonin test or thyroid ultrasound as routine screening.” The Wegovy and Zepbound labels say routine monitoring with either is of uncertain value for early detection of MTC.
- “Compounded or oral versions avoid the issue.” Foundayo’s label has its own contraindication for MTC and MEN 2. For compounded products, see how compounded semaglutide differs from Wegovy; a compounded product is not an FDA-approved drug and does not come with the approved label.
Questions to ask your prescriber
- Do my personal or family histories include medullary thyroid cancer, MEN 2 or other endocrine tumors?
- I have a thyroid nodule or a thyroid condition. Does that change your recommendation?
- Which symptoms should make me call you, and how quickly?
- If I have a neck lump or hoarseness that does not go away, who should evaluate it?
- How will you decide whether to continue my medicine over the long term?
Choosing a provider that screens for thyroid history
The thyroid warning is one reason intake quality matters when you start a GLP-1 online. If you are comparing services, our online GLP-1 telehealth platforms roundup and most trusted GLP-1 providers page are good places to begin, and our clinical quality comparison of top GLP-1 providers looks at medical oversight specifically. For brand-name medicines, see brand-name GLP-1 telehealth; for compounded options, compounded semaglutide providers. Provider-level write-ups, such as Ro pricing, Hims & Hers pricing, and whether Mochi Health is legit, show what each service says about its process. Browse everything in the GLP-1 provider directory. Our provider pages are editorial resources, not recommendations; see our advertiser disclosure and editorial standards for how they are produced.
Questions people ask
Is the thyroid warning on all GLP-1 medicines?
The Wegovy and Zepbound labels carry a boxed warning, and the Foundayo label contraindicates the same history and, as retrieved, carries a boxed warning too. Labels for other medicines in this class can differ, so check the label of the specific product you are prescribed.
Should I be screened for thyroid cancer before starting?
The labels do not describe routine calcitonin or ultrasound screening and say such monitoring is of uncertain value for early detection of MTC. They do rely on you and your prescriber reviewing your personal and family history before you start.
What if a relative has had a different kind of thyroid cancer?
The contraindication refers to medullary thyroid carcinoma and MEN 2. Tell your prescriber about any family cancer history so they can judge whether it applies and whether more questions are needed.
What should I do if I notice a neck lump or hoarseness?
Report it to your prescriber, as the labels advise. Do not stop or change a prescribed medicine without their instructions unless you have been told to seek emergency care.
Sources
- U.S. FDA labeling, Wegovy prescribing information (revised 06/2026), boxed warning, sections 4 and 5.1, checked 7 October 2026.
- U.S. FDA labeling, Zepbound prescribing information (revised 08/2026), boxed warning, sections 4 and 5.1, checked 7 October 2026.
- U.S. FDA labeling, Foundayo prescribing information (revised 07/2026), sections 4 and 17, checked 7 October 2026.
- Baxter SM et al., Glucagon-Like Peptide 1 Receptor Agonists and Risk of Thyroid Cancer: An International Multisite Cohort Study, Thyroid, January 2025 (DOI 10.1089/thy.2024.0387).
- American Thyroid Association, Medullary Thyroid Cancer, checked 7 October 2026.
Medical disclaimer. This article is informational and is not medical advice. It does not replace a conversation with your prescriber, who knows your personal and family history. Do not start, stop or change a prescribed medicine without instructions from your prescriber, and seek urgent care for difficulty breathing or swallowing.
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