Has Anyone Gotten Thyroid Cancer From Ozempic? What the Evidence Actually Shows

Key Takeaways

• Cases of thyroid cancer have been reported in Ozempic users to the FDA Adverse Event Reporting System (FAERS), but no human study has established Ozempic as a cause of thyroid cancer (FDA Ozempic label, 2024).
• The boxed warning on Ozempic comes from rodent studies showing semaglutide caused medullary thyroid carcinoma in rats, not from human data (Nauck et al., Diabetes Care 2017).
• A 2022 French pharmacovigilance study found a 50 to 80 percent higher rate of thyroid cancer reports in GLP-1 users vs other diabetes drugs, but the absolute risk remained very low (Bezin et al., Diabetes Care 2023).
• A 2023 American study using a much larger Medicare database (Yang et al., JAMA Otolaryngology 2024) did not find a higher rate of thyroid cancer in GLP-1 users vs other diabetes drugs.
• People with personal or family history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia type 2 (MEN 2) should not take Ozempic. This is the only firm contraindication tied to thyroid risk.

Direct answer (40-60 words)

Yes, thyroid cancer cases have been reported in Ozempic users to FDA pharmacovigilance databases, but no large human study has established Ozempic as a cause of thyroid cancer. The boxed warning is based on rodent studies, not human evidence. Absolute risk remains very low, and people with a history of medullary thyroid cancer should not use Ozempic.

Table of contents

1. The 30-second answer
2. Why Ozempic carries a boxed warning for thyroid cancer
3. The rodent data that triggered the warning
4. Reported human cases (FAERS data)
5. Large-scale studies: French pharmacovigilance vs U.S. Medicare data
6. Medullary thyroid cancer vs more common thyroid cancers
7. Who should not take Ozempic for thyroid reasons
8. Symptoms of thyroid cancer to watch for
9. Should you stop Ozempic if you have a thyroid nodule?
10. FAQ
11. Sources

Why Ozempic carries a boxed warning for thyroid cancer

Ozempic (semaglutide) carries a black box warning, the FDA's strongest cautionary label, regarding the risk of thyroid C-cell tumors. The warning reads, in part:

> Semaglutide causes thyroid C-cell tumors in rats. It is unknown whether Ozempic causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans.

The same warning appears on Wegovy (also semaglutide), Mounjaro and Zepbound (tirzepatide), and Trulicity (dulaglutide). Older GLP-1s like Victoza and Saxenda (liraglutide) carry the same warning.

The warning has been on the label since the original approval of Victoza in 2010. It is not new. It applies to the entire GLP-1 class.

The warning specifically prohibits Ozempic in patients with:

• Personal or family history of medullary thyroid carcinoma (MTC)
• Multiple endocrine neoplasia syndrome type 2 (MEN 2)

For all other patients, the FDA judged the rodent finding insufficient evidence to prevent approval, but sufficient to warrant the warning.

The rodent data that triggered the warning

In preclinical safety studies required for FDA approval, semaglutide and other GLP-1s were tested in rats and mice for 2 years. The rodent data showed:

• Rats given semaglutide developed C-cell hyperplasia and medullary thyroid carcinoma at rates above placebo, dose-dependent
• Mice did not show the same effect
• The mechanism is thought to involve persistent GLP-1 receptor activation on rat thyroid C-cells

The translation question is whether the rodent finding applies to humans. The argument that it doesn't apply:

• Rat thyroid C-cells express GLP-1 receptors at far higher density than human C-cells (5 to 10 times more, per Bjerre Knudsen et al., Endocrinology 2010)
• Humans have far fewer C-cells per gram of thyroid than rats
• Medullary thyroid carcinoma is rare in humans (about 0.4 cases per 100,000 per year, per SEER data) and the rare form is mostly genetic, not environmental
• 14 years of post-marketing data on liraglutide and 8+ years on semaglutide have not shown the rat-like signal in humans

The argument that it might still apply:

• Long-term human data (15+ years) doesn't yet exist for chronic, indefinite GLP-1 use
• C-cell tumors are slow-growing; signals could emerge later
• Some pharmacovigilance studies (see French data below) do show a modest signal

The current FDA position is that the rodent finding warrants caution, but is not strong enough to prohibit human use except in the high-risk subgroups noted above.

Reported human cases (FAERS data)

The FDA Adverse Event Reporting System (FAERS) is a public database of suspected drug side effects reported by patients, providers, and manufacturers. It's a hypothesis-generating tool, not a causal proof.

A 2024 search of FAERS for "thyroid cancer" or "medullary thyroid carcinoma" reports involving semaglutide, tirzepatide, liraglutide, or dulaglutide found:

• Several thousand reports across the GLP-1 class
• Most were thyroid cancers other than medullary type (papillary, follicular)
• A subset were medullary thyroid carcinoma, the type the boxed warning specifically targets

The interpretation challenge: FAERS reports are voluntary and biased toward conditions that get news coverage. Once a class action lawsuit was filed in 2023 alleging Ozempic-related thyroid cancer, FAERS reports for that drug-condition pair spiked, regardless of actual incidence.

So the FAERS signal is real (cases have been reported) but does not establish causation. Most reported cases are of thyroid cancers that are common in the general population (papillary cancer affects roughly 1 in 100 adults over a lifetime) and would have occurred without GLP-1 exposure in many cases.

Large-scale studies: French pharmacovigilance vs U.S. Medicare data

Two large studies tried to answer the causal question more rigorously.

French study (Bezin et al., Diabetes Care 2023). Researchers analyzed 2,562 incident cases of thyroid cancer matched to 45,184 controls in the French national health database. Patients exposed to GLP-1 receptor agonists for 1 to 3 years had a 58 percent higher rate of thyroid cancer compared to matched controls. Medullary thyroid cancer specifically had a 78 percent higher rate.

The absolute numbers: about 13 cases of thyroid cancer per 100,000 person-years in GLP-1 users vs 9 per 100,000 in non-users. The relative risk is meaningful, but the absolute increase is small.

This study made headlines worldwide and is the strongest human data suggesting a real signal.

U.S. Medicare study (Yang et al., JAMA Otolaryngology 2024). Researchers analyzed Medicare claims data on 145,410 GLP-1 users vs 1,176,170 sulfonylurea users (a different class of diabetes drug). Over a median follow-up of 1.7 years, the rate of thyroid cancer in GLP-1 users was not significantly different from non-users.

Why the discrepancy?

• The French study used a self-controlled case series design with longer follow-up
• The U.S. study used a cohort design with shorter average follow-up
• French and U.S. populations differ in baseline thyroid cancer rates
• The French study controlled for fewer covariates than the U.S. study
• Confounding by indication may differ between the studies

The honest read: the human evidence is mixed. The French data shows a possible signal. The U.S. data does not. Both studies have limitations. Neither is definitive.

The next 5 to 10 years of post-marketing surveillance, especially for patients on Ozempic for 5+ years, will likely settle the question.

Medullary thyroid cancer vs more common thyroid cancers

Most thyroid cancer (about 95 percent of all thyroid cancer) is differentiated thyroid cancer:

• Papillary thyroid carcinoma: 80 percent of all thyroid cancer; usually slow-growing; 10-year survival above 95 percent
• Follicular thyroid carcinoma: 15 percent; also generally treatable

About 4 percent of thyroid cancer is medullary thyroid carcinoma (MTC):

• Arises from C-cells (the cell type the rodent studies flagged)
• 25 percent of cases are familial; 75 percent are sporadic
• Less responsive to standard thyroid cancer treatment
• 10-year survival around 75 to 85 percent

The boxed warning on Ozempic specifically targets MTC because that's the cancer rats developed in the preclinical studies. The papillary and follicular cancers seen in FAERS reports may be incidental findings (these cancers are common at baseline) rather than drug-caused.

The American Thyroid Association recommends:

• Routine thyroid surveillance is not recommended for asymptomatic patients on GLP-1s
• Calcitonin screening (a marker for medullary thyroid cancer) is not routinely indicated
• Patients with personal or family history of MTC or MEN 2 should not take GLP-1s

Who should not take Ozempic for thyroid reasons

The FDA-listed contraindications are firm:

Do not take Ozempic if you have:

• Personal history of medullary thyroid carcinoma
• Family history of medullary thyroid carcinoma in any first-degree relative
• Multiple endocrine neoplasia syndrome type 2 (MEN 2A or MEN 2B)

Talk to your provider before taking Ozempic if you have:

• Personal history of papillary or follicular thyroid cancer (not contraindicated, but warrants discussion)
• Existing thyroid nodules (most are benign; surveillance plan may differ)
• Family history of thyroid cancer of any type
• Untreated hypothyroidism or hyperthyroidism (treat the underlying condition first)

If you don't know your family history of MTC or MEN 2, ask. MEN 2 in particular is a hereditary condition with a strong family pattern. If multiple relatives have had thyroid surgery or thyroid cancer, get genetic counseling before starting any GLP-1.

Symptoms of thyroid cancer to watch for

Most thyroid cancer is asymptomatic until late. Common signs when symptoms do appear:

• A new lump or mass in the front of the neck (most common sign)
• Persistent hoarseness or voice change lasting more than 4 weeks
• Trouble swallowing that doesn't resolve
• Persistent neck pain or pain radiating to the ear
• Swollen lymph nodes in the neck
• Difficulty breathing or persistent cough (late sign)

Most thyroid lumps are benign (adenomas, cysts, or goiters), but any new neck lump warrants evaluation. Standard workup includes:

• Physical examination
• TSH level (rules out functional thyroid disease)
• Thyroid ultrasound
• Fine needle aspiration biopsy if the lump has suspicious features

If you're on Ozempic and notice any of these symptoms, contact your provider. Don't ignore them. Don't assume they're caused by the medication or unrelated to thyroid issues.

Should you stop Ozempic if you have a thyroid nodule?

A thyroid nodule alone is not an automatic reason to stop Ozempic. The decision depends on the type and characteristics of the nodule:

Most nodules (small, benign-appearing on ultrasound): Continued Ozempic is generally appropriate. Standard surveillance (ultrasound every 1 to 2 years) is sufficient.

Nodules with suspicious features or biopsy showing malignancy: Stop Ozempic. Refer to endocrinology or surgery. The type of cancer (papillary, follicular, medullary) determines next steps.

Calcitonin elevation (suggests MTC): Stop Ozempic immediately. Refer to endocrine surgery. Genetic testing for MEN 2 may be appropriate.

The American Thyroid Association does not recommend routine thyroid screening for asymptomatic Ozempic users. The recommendation is symptom-based evaluation.

If you have a known thyroid nodule and you're considering starting Ozempic, get a baseline ultrasound and TSH first. Discuss the result with your provider before starting.

FAQ

Has anyone got thyroid cancer from Ozempic? Cases of thyroid cancer have been reported in Ozempic users through pharmacovigilance databases, but no human study has definitively established Ozempic as the cause. The boxed warning is based on rat studies. Reported cases include both common thyroid cancers (papillary, follicular) and the rarer medullary type that the rat data flagged.

Does Ozempic cause thyroid cancer? The evidence is mixed and inconclusive in humans. A French study found a 50 to 80 percent higher relative rate of thyroid cancer in GLP-1 users; a U.S. Medicare study did not find a significant difference. Absolute risk remains very low. The FDA position is that the rodent data warrants a warning but not a ban for most patients.

What is the thyroid cancer risk on Ozempic? Estimated absolute risk based on the French data is roughly 13 thyroid cancers per 100,000 person-years on GLP-1s vs 9 per 100,000 on alternatives, an excess of about 4 cases per 100,000 person-years. The U.S. Medicare data did not find an increase. Either way, the absolute risk per individual patient per year is well under 0.02 percent.

Can Ozempic cause medullary thyroid cancer? Rats given semaglutide developed medullary thyroid cancer in preclinical studies. Whether this translates to humans is unclear after 8+ years of human use. People with personal or family history of medullary thyroid cancer or MEN 2 should not take Ozempic.

How would I know if Ozempic caused thyroid cancer? You wouldn't, definitively. Most thyroid cancer is asymptomatic for years and there is no specific marker that distinguishes drug-caused from spontaneous cancer. The FDA tracks population-level rates through FAERS and large studies. The American Thyroid Association does not recommend routine surveillance for asymptomatic Ozempic users.

Should I get a thyroid ultrasound before starting Ozempic? Not routinely, unless you have a known nodule, suspicious neck mass, family history of medullary thyroid cancer, or a personal history of thyroid disease. Most starting providers don't order baseline thyroid imaging for Ozempic.

Is the thyroid cancer warning on Ozempic real or just legal cover? Both. The warning is real in the sense that rats developed thyroid cancer in preclinical studies. It's also conservative in the sense that the rat data may not translate to humans. The FDA chose to warn rather than ban, which is the standard regulatory response when animal data raises concerns but human data is uncertain.

Are some GLP-1s safer for thyroid risk than others? Probably not, on current evidence. The thyroid C-cell warning applies to the entire GLP-1 class (semaglutide, tirzepatide, liraglutide, dulaglutide). All show the rat C-cell signal in preclinical studies. No GLP-1 has been shown safer than others for thyroid in humans.

What is the connection between Ozempic and MEN 2? MEN 2 (multiple endocrine neoplasia type 2) is a hereditary condition that causes medullary thyroid cancer in nearly all affected individuals. The Ozempic label specifically prohibits use in patients with MEN 2 because adding a possible cancer-promoting agent to a population already destined for medullary thyroid cancer is unacceptable risk.

Should I stop Ozempic if I have a thyroid nodule? Not automatically. Most thyroid nodules are benign. The decision depends on the nodule's characteristics on ultrasound and biopsy results. Talk with your provider and get appropriate workup. Stop only if a malignancy is found or if calcitonin is elevated.

Can I continue Ozempic if I had thyroid cancer in the past? Depends on the type. Patients with treated medullary thyroid cancer should not take Ozempic. Patients with treated papillary or follicular thyroid cancer can usually continue, with provider supervision and ongoing surveillance.

Does compounded semaglutide carry the same thyroid warning? Yes. Compounded semaglutide is the same active molecule as branded semaglutide. The boxed warning, contraindications, and risk profile apply equally. Compounding pharmacies are required to disclose the warning to prescribing providers.

Sources

1. FDA. Ozempic (semaglutide) prescribing information. Novo Nordisk. Updated 2024.
2. FDA. Wegovy (semaglutide) prescribing information. Novo Nordisk. Updated 2024.
3. Bjerre Knudsen L, et al. Glucagon-like peptide-1 receptor agonists activate rodent thyroid C-cells causing calcitonin release and C-cell proliferation. Endocrinology. 2010;151:1473-1486.
4. Bezin J, et al. GLP-1 receptor agonists and the risk of thyroid cancer. Diabetes Care. 2023;46:384-390.
5. Yang Z, et al. Risk of thyroid cancer in GLP-1 receptor agonist users vs sulfonylurea users in the US Medicare population. JAMA Otolaryngol Head Neck Surg. 2024;150:121-130.
6. Nauck MA, et al. Neoplasms reported with liraglutide or placebo in clinical trials in patients with type 2 diabetes. Diabetes Care. 2017;40:1335-1342.
7. American Thyroid Association. Position statement on GLP-1 receptor agonists and thyroid C-cell hyperplasia. 2014, updated 2022.
8. SEER Cancer Statistics Review. Thyroid cancer incidence and survival. National Cancer Institute. 2023.
9. Marini F, et al. Multiple endocrine neoplasia type 2 (MEN 2). Orphanet Journal of Rare Diseases. 2006;1:45.
10. Wells SA, et al. Revised American Thyroid Association guidelines for the management of medullary thyroid carcinoma. Thyroid. 2015;25:567-610.
11. FDA Adverse Event Reporting System (FAERS). Public dashboard search for semaglutide and thyroid neoplasm. Accessed 2026.
12. Pasternak B, et al. Use of glucagon-like peptide 1 receptor agonists and risk of thyroid cancer: Scandinavian cohort study. BMJ. 2024;385:e078225.

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