A meta-analysis of 64 randomized trials found a small but statistically significant 52% increase in relative thyroid cancer risk with GLP-1 receptor agonists, though the absolute risk increase was very small.
1 in 1,349The estimated number of patients who would need to be treated with a GLP-1 drug for 5 years for one additional thyroid cancer case to occur
What the researchers found
Across 64 randomized controlled trials, GLP-1 receptor agonist treatment was associated with a statistically significant increase in overall thyroid cancer risk, with a Mantel-Haenszel odds ratio of 1.52 (95% CI: 1.01–2.29, p=0.04). There was no significant heterogeneity between studies (I²=0%).
The fragility index was just 1, meaning a single event change would eliminate statistical significance. The 5-year number needed to harm was 1,349 — meaning approximately 1 extra thyroid cancer case per 1,349 patients treated for 5 years.
When restricted to trials lasting at least 104 weeks, the association strengthened slightly (OR 1.76, 95% CI: 1.00–3.12). However, neither papillary thyroid cancer (OR 1.54, p=0.22) nor medullary thyroid cancer (OR 1.44, p=0.55) reached significance individually.
Why it matters
With tens of millions of people now taking GLP-1 drugs like Ozempic and Mounjaro, even a small increase in cancer risk has enormous public health implications. Rodent studies had previously shown thyroid tumors with GLP-1 drugs, but human data has been unclear. This is one of the largest meta-analyses to specifically examine thyroid cancer risk with GLP-1 receptor agonists using only randomized trial data — the gold standard for causality assessment.
How the study worked
This was a systematic review and meta-analysis of randomized controlled trials comparing any GLP-1 receptor agonist to any comparator. Included trials had to last at least 52 weeks and report adverse event incidence. Researchers collected all thyroid cancer cases across 64 eligible trials and calculated pooled odds ratios using the Mantel-Haenszel method. They also performed subgroup analyses by cancer subtype and trial duration.
What this study cannot tell us
The fragility index of 1 means the overall finding is statistically fragile — a single event change would make it non-significant. Most trials were designed to study diabetes or weight loss, not cancer, so thyroid cancer detection may have been inconsistent across studies. The longest trials were still relatively short for cancer development, and the subtype-specific analyses (papillary, medullary) were underpowered. The meta-analysis cannot determine whether specific GLP-1 drugs carry more or less risk than others.
How to read the evidence
This is a systematic review and meta-analysis of 64 randomized controlled trials — among the highest levels of evidence. However, the fragility index of 1 significantly weakens confidence in the finding, and the individual subtype analyses did not reach significance. The overall quality is high but the conclusion is tentative.
When this study was published
Published in 2024, this is a very recent analysis incorporating the latest GLP-1 trial data. Given the explosive growth in GLP-1 prescribing, this represents the most current pooled assessment available from randomized trials.
The bigger picture
The GLP-1 drug class has become the fastest-growing pharmaceutical category in history, prescribed for diabetes, obesity, and increasingly being studied for heart disease, kidney disease, and addiction. Regulatory agencies have required thyroid cancer warnings on GLP-1 drug labels based on animal data, but human evidence has been inconsistent. This meta-analysis provides the most rigorous evidence to date of a small but real signal, while also showing the absolute risk is low. The debate now shifts to whether longer-term surveillance will confirm or refute this finding as more patients take these drugs for years or decades.
Questions still open
- Will longer-duration observational studies with millions of patients confirm this small increase in thyroid cancer risk?
- Do specific GLP-1 receptor agonists (e.g., semaglutide vs. liraglutide) differ in their thyroid cancer risk profiles?
- Is the increased detection simply due to more medical surveillance in GLP-1 trial participants rather than a true biological effect?
Common questions
Should I stop taking my GLP-1 medication because of thyroid cancer risk?
Is this the same thyroid cancer risk that's listed on Ozempic's label?
Read the original research
Glucagon-like peptide-1 receptor agonists and risk of thyroid cancer: A systematic review and meta-analysis of randomized controlled trials.
Diabetes, obesity & metabolism, 26(3), 891-900
Citation
Silverii, Giovanni Antonio; Monami, Matteo; Gallo, Marco; Ragni, Alberto; Prattichizzo, Francesco; Renzelli, Valerio; Ceriello, Antonio; Mannucci, Edoardo. (2024). Glucagon-like peptide-1 receptor agonists and risk of thyroid cancer: A systematic review and meta-analysis of randomized controlled trials.. Diabetes, obesity & metabolism, 26(3), 891-900. https://doi.org/10.1111/dom.15382