No! Weight-Loss Injections Do Not Cause Thyroid Cancer

Concerns have recently been raised about thyroid cancer risk with GLP-1 receptor agonists (GLP-1 RAs), commonly known as weight-loss injections. However, one of the largest studies to date has found no significant association between the use of these drugs and thyroid cancer. The study was published on 8 January 2025 in Thyroid . This article examines the details of the study and what its findings mean.

A Multinational Study of 2.6 Million People

This large study covered data collected between 2007-2023 in six countries: Canada, Denmark, Norway, South Korea, Sweden and Taiwan.

It included 98,147 people with type-2 diabetes who used GLP-1 RAs and a comparator group of 2,488,303 people who used dipeptidyl peptidase 4 inhibitors (DPP-4i). The groups were matched to ensure that they began these drugs at similar stages of diabetes and at comparable times.

Findings: No Increase in Thyroid Cancer Risk

Median follow-up ranged from 1.8 to 3.0 years in the GLP-1 RA group and from 2.8 to 6.8 years in the DPP-4i group. Analyses found no significant difference in thyroid cancer risk between patients using GLP-1 RAs and those using DPP-4i (HR: 0.81; CI: 0.59-1.12). Results were consistent across all study sites.

Subgroup Analyses

• Analyses of subgroups defined by factors such as age, GLP-1 RA type and cumulative drug dose found no increase in thyroid cancer risk.

• Among women using GLP-1 RAs, risk appeared lower (HR: 0.62), whereas in men it appeared somewhat higher (HR: 1.32).

• Rare types such as medullary thyroid cancer could not be analyzed, which also indicated that these cancers were extremely rare.

What Do the Results Mean?

Lead author Anton Pottegard said that the findings were reassuring regarding current concerns: “We cannot offer a guarantee for 20 years from now, but we see no risk in the data currently available.”

Juan Brito and colleagues at Mayo Clinic noted that the short follow-up periods were insufficient to assess long-term risks, while acknowledging the important contribution of the study. Brito emphasized that some increases in thyroid cancer risk could reflect factors that are difficult to record accurately, such as body mass index and weight.

Commentary

This large and carefully conducted study provides important evidence that GLP-1 RA drugs are not significantly associated with thyroid cancer in the short term. These findings offer important reassurance to patients with diabetes who use these drugs and to people seeking weight management. Nevertheless, the need for further studies of long-term effects should not be overlooked.