Thyroid cancer diagnoses in the United States have increased significantly over recent decades, largely due to more frequent use of advanced imaging techniques that detect small, often harmless thyroid nodules1 . Despite this rise in incidence, the death rate from thyroid cancer has remained very low and stable, indicating that many detected cases may not impact patient health2 . Medications like Ozempic, a glucagon-like peptide-1 receptor agonist (GLP-1RA), have raised concerns about thyroid cancer risk, but current evidence suggests these drugs do not cause a meaningful increase in thyroid cancer among humans1 .
GLP-1 Medications and Thyroid Cancer
GLP-1 receptor agonists, including Ozempic, Wegovy, and Rybelsus, are medications primarily used to treat type 2 diabetes and obesity by reducing appetite and slowing gastric emptying3 . These drugs stimulate GLP-1 receptors, improving blood sugar control and promoting weight loss3 . However, concerns about thyroid cancer risk emerged from animal studies showing that GLP-1RAs caused thyroid C-cell hyperplasia and medullary thyroid cancer (MTC) in rodents4 . MTC is a rare form of thyroid cancer arising from parafollicular C cells and accounts for about 3–4% of thyroid cancers in humans5 .
Due to these animal findings, the U.S. Food and Drug Administration (FDA) issued a black box warning advising patients with a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2 (MEN2) to avoid GLP-1RAs4 5. Despite this, large human cohort studies have not demonstrated an increased risk of thyroid cancer with GLP-1RA use6 7. For example, a large retrospective cohort study of over 350,000 adults with type 2 diabetes found no significant overall increase in thyroid cancer risk among GLP-1RA users compared to users of other diabetes medications8 . The study did observe a higher rate of thyroid cancer diagnosis within the first year of GLP-1RA initiation, but this was attributed to increased thyroid ultrasound screening rather than a causal effect8 .
Key points about GLP-1 medications and thyroid cancer risk include:
- Rodent studies showed GLP-1RAs cause C-cell proliferation linked to medullary thyroid cancer, leading to FDA black box warnings4 5.
- Human studies have not confirmed increased thyroid cancer risk with GLP-1RA use6 7.
- GLP-1RA users have higher rates of thyroid ultrasound screening, which may explain early increases in thyroid cancer diagnoses1 8.
- The majority of thyroid cancers detected in these studies are likely indolent nodules found through enhanced surveillance1 .
- The FDA warning applies specifically to medullary thyroid cancer risk and patients with genetic predispositions, not to the more common papillary thyroid cancer5 .
“At face value, GLP-1s did slightly increase the risk of thyroid cancer diagnoses. When we dove in deeper, we found that this increase in risk was seen only in the first year, which is important because cancer takes a long time to develop. This raised our suspicions.”
— Rozalina McCoy, MD, University of Maryland School of Medicine9
Causes of Thyroid Cancer Overdiagnosis
The sharp rise in thyroid cancer incidence in the U.S. over recent decades is largely explained by overdiagnosis—the detection of cancers that would not have caused symptoms or death during a patient’s lifetime1 10. This phenomenon is driven by the widespread use of sensitive imaging techniques such as ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI), which frequently identify small, asymptomatic thyroid nodules11 12.
Many of these nodules are clinically insignificant and indolent, meaning they grow slowly or not at all and are unlikely to affect patient outcomes10 11. Despite the increasing number of thyroid cancer diagnoses, mortality rates have remained stable and very low, supporting the conclusion that many detected cancers represent overdiagnosis rather than a true increase in disease burden2 11.
The most common type of thyroid cancer is papillary thyroid cancer, which accounts for approximately 80% of cases and has an excellent prognosis with a five-year survival rate exceeding 99% 1011. Other types include follicular, medullary, and anaplastic thyroid cancers, with medullary thyroid cancer representing only 3–5% of cases13 .
Factors contributing to thyroid cancer overdiagnosis include:
- Increased use of diagnostic imaging for unrelated conditions leading to incidental thyroid nodule detection12 .
- Enhanced surveillance and screening practices, especially in populations using GLP-1 medications due to FDA warnings1 3.
- Detection of small, early-stage tumors that may never progress to cause symptoms14 .
- Changes in professional guidelines encouraging more thyroid evaluations15 .
- Improved molecular testing allowing identification of genetic mutations, which influences treatment decisions but may also increase detection13 .
Thyroid cancer tends to be diagnosed at higher rates due to the common use of imaging tests, like ultrasound. Screenings for unrelated conditions can pick up thyroid nodules that are cancerous but do not cause symptoms.
Thyroid Cancer Risk for GLP-1 Users
For people using GLP-1 receptor agonists such as Ozempic, the risk of developing thyroid cancer is generally low and not significantly elevated compared to users of other diabetes medications1 6. The increased thyroid cancer diagnoses observed shortly after starting GLP-1 therapy are thought to result from detection bias due to more frequent thyroid ultrasound screenings rather than a true increase in cancer risk1 16.
The FDA’s black box warning on GLP-1RAs may lead to heightened vigilance among patients and physicians, prompting more thyroid imaging and thus more incidental findings of harmless nodules17 1. This increased screening likely contributes to the overdiagnosis phenomenon in this population1 .
If you have medullary thyroid cancer or genetic testing that puts you at risk for thyroid cancer, or you have a family member who has medullary thyroid cancer, they say you shouldn't use these drugs.
— Bryan Haugen, MD, University of Colorado Cancer Center5
Papillary thyroid cancer, the most common subtype, has a near 100% five-year survival rate, underscoring its favorable prognosis even when diagnosed10 11. For patients with differentiated thyroid cancer, including papillary type, the benefits of GLP-1 medications in improving metabolic health and reducing obesity-related risks often outweigh the potential thyroid cancer concerns5 .
Important considerations for GLP-1 users regarding thyroid cancer risk:
- No clear evidence links GLP-1RA use to increased risk of medullary or differentiated thyroid cancers in humans1 6.
- Early increases in thyroid cancer diagnoses among GLP-1 users are likely due to increased ultrasound screening1 16.
- Papillary thyroid cancer is generally slow-growing and has excellent survival outcomes10 11.
- Patients with personal or family history of medullary thyroid cancer or MEN2 should avoid GLP-1RAs per FDA guidance4 5.
- Physicians balance medication safety with avoiding unnecessary cancer diagnoses by monitoring patients appropriately6 .
Overall, the results have been mixed, with some trials saying that there’s no increased risk and some trials saying that there’s a slight increased risk. But there has been really no evidence to show that there is a substantial risk of non-medullary thyroid cancer associated with these weight loss drugs.
— Ryan McSpadden, MD, Roswell Park Comprehensive Cancer Center3
- Discuss any personal or family history of thyroid cancer with your healthcare provider6 .
- Understand that increased thyroid screening may detect harmless nodules that do not require treatment1 .
- Regular thyroid physical exams and routine lab tests can help monitor thyroid health13 .
- If you are on thyroid hormone replacement, medication doses may need adjustment due to altered absorption with GLP-1 use3 .
- Focus on the overall health benefits of GLP-1 medications, including improved blood sugar control and weight loss3 .
