A new study found that weight loss drugs like Ozempic and Wegovy may be contributing to a national trend of thyroid cancer overdiagnosis.

The research, published in JAMA Otolaryngology—Head & Neck Surgery in January, found that people on glucagon-like peptide-1 (GLP-1) receptor agonists are more likely to receive a thyroid cancer diagnosis than the general population. 

However, it’s unlikely that the medication is actually causing cancer. Instead, GLP-1 users are more apt to get screened for the disease, likely because previous research has connected the drugs with a higher risk for thyroid cancer, study author Rozalina McCoy, MD, an associate professor and the associate division chief for clinical research in the Division of Endocrinology, Diabetes, and Nutrition at the University of Maryland School of Medicine, told Health.

“We are finding more cancers, and this is really because we’re looking for them and we’re getting more ultrasounds,” she said.

These thyroid screenings commonly pick up harmless nodules, leading to an unnecessary cancer diagnosis. This is also a problem in the general population. A study published in early February found that thyroid cancer has been overdiagnosed for over a decade, likely due to the increase in medical imaging.

“What we found was that although the incidence of thyroid cancer stopped rising after 2009, the rates of overdiagnosed thyroid cancers have essentially stayed the same,” Zachary Zumsteg, MD, an associate professor of radiation oncology and biomedical sciences at Cedars-Sinai Cancer Institute and a senior author of that study, told Health in an email. “Thyroid cancer continues to be overdiagnosed at peak levels without any significant improvement.”

The researchers of the JAMA study initially set out to revisit the question of whether GLP-1 drugs increased the risk of thyroid cancer, McCoy said.

A 2010 animal study found that long-term exposure to liraglutide, a GLP-1 receptor agonist, increased rodents’ risk of medullary thyroid cancer, the rarest form, making up 3% to 4% of all human cases. This research led to a black box warning on the medication.

Research in humans found no additional risk of thyroid cancer in people using GLP-1s.

To further assess the link between GLP-1 use and thyroid cancer, McCoy and her team analyzed data from 351,913 adults who had newly filled prescriptions for several medications, including GLP-1s. All participants had type 2 diabetes, were at moderate risk for heart disease, and did not have a history of thyroid cancer.

“At face value, GLP-1s did slightly increase the risk of thyroid cancer diagnoses,” McCoy said. “But when we dove in deeper, we found that this increase in risk was seen only in the first year [after starting GLP-1s], which is important because cancer takes a long time to develop. This raised our suspicions.”

To examine the potential for overdiagnosis, the researchers then checked if people on GLP-1s were more likely to get screened for thyroid cancer. “We found that patients treated with GLP-1s are much more likely to have a [thyroid] ultrasound,” McCoy said.

She and her colleagues concluded that the screenings were simply picking up existing nodules, most of which wouldn’t pose a threat if left undetected.

The study did have some limitations, McCoy said. Detailed patient information—including potential risk factors for thyroid cancer—wasn’t available. The researchers also didn’t know for sure why the patients were screened and diagnosed with thyroid cancer or which type and stage the cancer was.

In the general public, experts said thyroid cancer tends to be overdiagnosed because of the prevalence of medical imaging, like CT scans and MRIs. 

Screenings for unrelated conditions can pick up thyroid nodules that are technically cancerous but asymptomatic or clinically insignificant. 

“Had they not been found, that wouldn’t have changed much of anything from the patient’s perspective,” Richard Siegel, MD, an endocrinologist and co-director of the Diabetes and Lipid Center at Tufts Medical Center, told Health.

“Mortality from thyroid cancer as a whole continues to be very, very low,” Siegel added. While thyroid cancer survival rates vary depending on the type and stage, papillary thyroid cancer—the most common type—has a 99.5% five-year survival rate. “Ultimately, you’re getting a lot of early diagnosis of nodules,” Siegel said.

McCoy suspected that people on GLP-1s were experiencing a similar effect. She said the black box warning on GLP-1 drugs may make patients and physicians more hypervigilant, leading to increased screenings for thyroid cancer and early diagnoses for harmless nodules.

“They all stem from wanting to do our due diligence and make sure that we use these medications safely and don’t miss something sinister,” McCoy added.

Experts agreed that patients on GLP-1s are unlikely to have an increased risk of thyroid cancer. “The evidence we have that raises suspicion is from animal studies that do not necessarily translate to people,” McCoy explained.

“I feel very confident telling my patients that they can safely take GLP-1s,” she added. “If they are worried about thyroid cancer, it should be for reasons other than a GLP-1.”

People may have an increased risk of thyroid cancer if they have a family history of the disease or a rare genetic disorder called multiple endocrine neoplasia type 2, or MEN2, Siegel said. Exposure to high levels of radiation can also elevate the chances of thyroid cancer, McCoy added. 

Experts recommend talking to your doctor if you’re concerned about your thyroid cancer risk. Still, for both GLP-1 users and the general population, experts stressed that the risk of thyroid cancer is low. “I tell my patients, ‘We’re victims of our own technology,’” Siegel said.