Reassuring Patients About Thyroid Risk with Ozempic
You should reassure your patient that while Ozempic (semaglutide) carries an FDA black box warning for thyroid C-cell tumors based on rodent studies, there is no established evidence that it causes thyroid cancer in humans, and it is contraindicated only if they have a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). 1
Key Points to Communicate
The Warning is Based on Animal Studies, Not Human Evidence
- Semaglutide caused thyroid C-cell tumors (adenomas and carcinomas) in mice and rats after lifetime exposure at clinically relevant doses. 1
- The human relevance of these rodent thyroid tumors has not been determined, and it remains unknown whether Ozempic causes medullary thyroid carcinoma in humans. 1
- While cases of MTC have been reported in patients treated with liraglutide (another GLP-1 receptor agonist), the data are insufficient to establish or exclude a causal relationship between MTC and GLP-1 receptor agonist use in humans. 1
Who Should NOT Take Ozempic
Ozempic is absolutely contraindicated in patients with: 1
- A personal history of medullary thyroid carcinoma
- A family history of medullary thyroid carcinoma
- Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
If your patient has none of these conditions, they are not in the contraindicated group. 1
Symptoms to Monitor
Counsel your patient to watch for symptoms of thyroid tumors and seek immediate evaluation if they develop: 1
- A mass in the neck
- Difficulty swallowing (dysphagia)
- Difficulty breathing (dyspnea)
- Persistent hoarseness
Routine Monitoring is Not Recommended
- Routine monitoring of serum calcitonin or thyroid ultrasound is of uncertain value for early detection of MTC in patients treated with Ozempic. 1
- Such monitoring may actually increase the risk of unnecessary procedures due to low test specificity for serum calcitonin and the high background incidence of thyroid disease in the general population. 1
- If serum calcitonin is measured and found to be significantly elevated (MTC patients usually have values >50 ng/L), further evaluation is warranted. 1
Clinical Context
The Real Thyroid Issue May Be Different
Recent evidence suggests that GLP-1 receptor agonists like semaglutide may affect thyroid hormone levels in patients already on levothyroxine replacement therapy, but this is unrelated to thyroid cancer risk: 2, 3
- Patients on stable levothyroxine doses who lose significant weight with semaglutide may develop iatrogenic hyperthyroidism requiring dose reduction. 2
- The mechanism is unclear but may relate to increased medication absorption, changes in gastric emptying, or the weight loss itself. 2, 3
Pretreatment Assessment Gaps
A 2025 study found that despite the FDA warning, pretreatment assessment for thyroid disease history is inadequately performed in clinical practice—only 1.8% of patients had proper disease history checks before starting semaglutide. 4
Practical Approach
Before prescribing, specifically ask about: 1
- Personal history of thyroid cancer (especially medullary type)
- Family history of thyroid cancer
- History of MEN 2 syndrome
If all answers are negative, the patient can safely proceed with Ozempic therapy. 1
Advise the patient to report neck masses, swallowing difficulties, breathing problems, or persistent hoarseness immediately, but emphasize that the actual human risk remains unproven. 1