Zepbound Does Not Cause Thyroid Cancer
There is no evidence that Zepbound (tirzepatide) causes thyroid cancer in humans, and no percentage can be provided because this association does not exist in clinical data. The confusion likely stems from the boxed warning on GLP-1 and dual GIP/GLP-1 receptor agonists regarding medullary thyroid carcinoma (MTC) observed in rodent studies, but this has not translated to human risk 1.
Critical Distinction: Rodent vs. Human Risk
- The thyroid cancer warning on tirzepatide (Zepbound) is based solely on rodent studies where C-cell tumors developed, not on any human cases 1
- Medullary thyroid cancer arises from parafollicular C-cells and represents only 4-5% of all thyroid cancers in humans 2
- Patients with a history of papillary thyroid cancer (the most common type, accounting for 80-90% of cases) are not contraindicated from using tirzepatide, according to guidance from the National Comprehensive Cancer Network 1
What the Evidence Actually Shows
- GLP-1 receptors have been discovered on human papillary thyroid carcinomas, but the impact on tumor growth remains unknown 2
- No clinical trials or post-marketing surveillance data have demonstrated an increased incidence of thyroid cancer in humans taking tirzepatide or similar medications 1
- The American College of Physicians and other medical societies indicate that GLP-1 receptor agonists or dual GIP/GLP-1 receptor agonists like tirzepatide are not contraindicated in patients with a history of papillary thyroid cancer 1
Clinical Recommendations for Patients Considering Zepbound
For patients with no thyroid cancer history:
- Tirzepatide can be used without specific thyroid cancer screening beyond standard care 1
- The boxed warning is a regulatory requirement based on animal data, not human evidence 2
For patients with prior papillary thyroid cancer:
- Patients should have completed appropriate initial treatment and be in an appropriate surveillance program for their risk category before starting tirzepatide 1
- Standard thyroid cancer surveillance should continue as recommended based on risk stratification, with no additional monitoring required specifically due to tirzepatide use 1
- High-risk patients may require more careful monitoring, though there is no evidence that tirzepatide increases recurrence risk 1
Important Caveats
- The only absolute contraindication is for patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), based on the rodent data and theoretical risk 2, 1
- For patients with concerns about thyroid cancer risk, the American Medical Association suggests considering FDA-approved alternatives without thyroid cancer concerns, such as phentermine, metformin, orlistat, and bariatric endoscopic procedures 2
- Patients with residual thyroid cells after thyroid cancer treatment should have careful consideration of risks and benefits, according to the American College of Radiology 2
The answer to "what percent of people get thyroid cancer due to Zepbound" is effectively zero based on current human data—no causal relationship has been established in clinical use 1.