New Research on GLP-1 Drugs and Thyroid Cancer

If you’ve been curious about GLP-1 drugs like Ozempic, but hesitated due to concerns over thyroid cancer, there’s some new research that might ease your worries. A study by doctors at the Clayman Thyroid Center in Florida reviewed existing medical literature and found no convincing evidence linking GLP-1 drugs to thyroid cancer in humans. However, for those with a family history of a specific, rare type of thyroid cancer, it’s still advisable to steer clear of these medications, in line with FDA recommendations.

“The best available human evidence does not show that GLP-1 receptor agonists cause common thyroid cancers, nor do they appear to influence the development of existing thyroid cancers,” the researchers noted in a white paper released recently.

GLP-1s and Thyroid Cancer Risk

GLP-1 medications have been around for about 20 years, but only recently have options like semaglutide (Ozempic and Wegovy) and tirzepatide (Mounjaro and Zepbound) gained traction as first-line treatments for obesity.

While these drugs are known to commonly result in gastrointestinal issues—think nausea, diarrhea, and constipation—they also come with a black box warning regarding the potential risk of medullary thyroid cancer (MTC). This warning was primarily based on studies conducted in rodents, leading scientists to explore whether a similar risk exists for people using these drugs.

The Clayman researchers analyzed clinical trial data, adverse event reports, and large-scale studies involving real patients. Overall, they found minimal evidence suggesting that GLP-1 usage correlates with a higher incidence of thyroid cancer. Some studies did report increased diagnoses of these cancers—or even unusual nodules that may turn cancerous—among GLP-1 users. However, the researchers believe this is likely due to something called detection bias.

People on GLP-1 drugs tend to visit their doctors more frequently, which often results in more thorough screenings for thyroid cancer. As a result, they might end up with more diagnosed cases, not necessarily because of the medication. In studies that have tried to address this bias—by looking at cancer diagnosis rates right after starting GLP-1s, when the drug wouldn’t realistically cause new cases—no significant links to thyroid cancer have been found.

“When diagnoses rise shortly after initiating a medication, that often indicates that something was already there,” said co-author Rashmi Roy in a statement from the center. “That is very different from a drug actually causing a new cancer.”

When to Avoid GLP-1 Drugs

The findings from this research are likely to reduce some of the fears that patients and healthcare providers have regarding GLP-1 medications and thyroid cancer, according to the researchers. They suggest that even the concern about MTC may be overstated.

Handling around 2,000 thyroid cancer cases each year, the Clayman Thyroid Center is one of the largest specialized clinics globally. Since the growing popularity of these drugs, they haven’t observed any increase in MTC cases specifically.

“In a practice that sees more thyroid cancer than anywhere else, we’re not witnessing a spike in MTC among GLP-1 users. This aligns with established research,” they commented.

Still, the researchers emphasize that their observations are largely anecdotal. Given the rarity of MTC—accounting for about 3% of thyroid cancers—large population studies would be necessary to truly confirm or refute an increased risk associated with GLP-1 usage. Thus, for now, they recommend that individuals with a personal or family history of MTC, or a related hereditary condition called MEN2, refrain from using these medications.

Like any medication, GLP-1s carry their own risks. Yet, it seems that thyroid cancer isn’t a significant concern associated with their use.