In patients with small thyroid cancers being monitored without surgery, taking GLP-1 drugs like semaglutide did not speed up tumor growth over a median of 25 months of use.
No growth difference (p=0.53)84% of thyroid tumors in patients on GLP-1 drugs remained stable over 5.5 years, comparable to the 92% stable rate in unexposed patients
What the researchers found
GLP-1 receptor agonists did not accelerate the growth of low-risk papillary thyroid carcinomas. After a median of 25 months on GLP-1RA therapy and 5.5 years of follow-up, 84.2% of tumors in the GLP-1RA group remained stable, compared to 92.1% in the unexposed group — a difference that was not statistically significant (p=0.53).
Among the two tumors in the GLP-1RA group that did grow, the drug did not alter their growth kinetics (they were already growing before GLP-1RA exposure). This provides early reassurance that GLP-1 drugs don't fuel thyroid cancer growth.
Why it matters
GLP-1 drugs like semaglutide and tirzepatide carry FDA-mandated warnings about thyroid C-cell tumors based on rodent studies. With millions of patients now taking these drugs, there's intense interest in whether they actually affect thyroid cancer risk in humans. This study specifically addresses whether GLP-1RAs make existing thyroid cancers grow faster — and finds no evidence they do.
The numbers in context
n=18 GLP-1RA patients (19 tumors) vs n=37 controls (38 tumors) · median 25 months GLP-1RA exposure · median 5.5 years follow-up · 84.2% stable on GLP-1RA vs 92.1% stable controls · p=0.53
How the study worked
Retrospective cohort study at a single tertiary center. 18 patients with small (≤1.5 cm) papillary thyroid carcinomas on active surveillance who were exposed to GLP-1RAs were matched 1:2 by BMI and tumor size to 37 unexposed patients. Researchers tracked tumor growth using diameter changes (≥3 mm) and volume changes (>72%). Volume doubling time was calculated for a subset of patients before and during GLP-1RA therapy.
Who was studied
Patients with low-risk papillary thyroid carcinomas (≤1.5 cm) undergoing active surveillance at a tertiary center
What this study cannot tell us
Very small sample size (18 exposed patients). Retrospective design at a single center. Only low-risk papillary thyroid carcinomas (≤1.5 cm) were studied — results may not apply to larger or more aggressive thyroid cancers. Median GLP-1RA exposure was only 25 months. The study was underpowered to detect small differences in growth rates.
How to read the evidence
This is a retrospective observational study with a small sample size (18 exposed patients). While the matched cohort design and long follow-up are strengths, the study is underpowered to detect subtle effects. It provides reassuring preliminary evidence but cannot definitively rule out a small risk.
When this study was published
Published in 2026. This is a very recent and timely study addressing one of the most pressing safety questions about GLP-1 drugs. As more patients take these medications, larger studies will likely follow.
The bigger picture
The thyroid cancer concern has been a cloud over GLP-1 drugs since their approval. Rodent studies showed these drugs caused thyroid C-cell tumors, leading to boxed warnings. But rodent thyroid biology differs significantly from humans. As GLP-1 prescriptions skyrocket into the tens of millions, real-world human safety data like this study — even though small — helps clarify whether the rodent signal translates to humans. So far, the answer appears to be no.
Questions still open
- Would longer GLP-1RA exposure (5+ years) reveal any effect on thyroid tumor growth that shorter exposure doesn't?
- Do these reassuring findings extend to medullary thyroid carcinoma, the type most concerning from rodent studies?
- Is there a difference in thyroid cancer outcomes between specific GLP-1 drugs (semaglutide vs. liraglutide vs. tirzepatide)?
Common questions
Should I stop my GLP-1 drug if I have a thyroid nodule?
Why do GLP-1 drugs carry a thyroid cancer warning if the evidence in humans is reassuring?
Read the original research
Effect of GLP-1 Receptor Agonists on Patients with Thyroid Carcinomas Undergoing Active Surveillance.
Journal of the Endocrine Society, 10(1), bvaf182
Citation
Patrizio, Armando; Newman, Samantha K; Tuttle, R Michael; Boucai, Laura. (2026). Effect of GLP-1 Receptor Agonists on Patients with Thyroid Carcinomas Undergoing Active Surveillance.. Journal of the Endocrine Society, 10(1), bvaf182. https://doi.org/10.1210/jendso/bvaf182