GLP-1s and Cancer: Thyroid Cancer, Pancreatitis and Other Cancers

The boxed warning on semaglutide (Ozempic, Wegovy) and tirzepatide (Zepbound, Mounjaro) is based on thyroid C-cell tumors in rats and mice; whether the drugs cause them in people is unknown. Human studies disagree: a French case-control study linked 1 to 3 years of GLP-1 use to more thyroid cancer, while a larger Scandinavian cohort of 145,410 users found no increase. Acute pancreatitis is a labeled but uncommon risk (0.2 cases per 100 patient-years on Wegovy in the weight trials). For other cancers, observational data so far point to similar or lower risk, not higher.

By Kymata Labs Editorial · Published Oct 11, 2026 · Updated Oct 11, 2026 · How we rank

Facts checked Oct 11, 2026 · Medical review pending

Quick answer

Thyroid cancer: grade D for harm in humans (rodent data only) plus mixed grade C human data. A French study found a higher risk after 1 to 3 years of use (hazard ratio 1.58); a Scandinavian cohort found none (hazard ratio 0.93) over about 4 years.
Who should not take one: anyone with a personal or family history of medullary thyroid carcinoma or MEN 2, per the labels.
Pancreatitis: confirmed in 4 Wegovy-treated patients (0.2 per 100 patient-years) versus 1 on placebo in the weight trials. Stop the drug and get care for severe, persistent stomach pain that may spread to the back.
Other cancers: in a US study of 1.65 million people with type 2 diabetes, GLP-1 users had lower rates of 10 of 13 obesity-linked cancers than insulin users, but not compared with metformin users, and kidney cancer was higher versus metformin (grade C).

What the boxed warning actually says

In rodents, semaglutide and tirzepatide caused dose- and duration-dependent thyroid C-cell tumors at exposures similar to human doses. The labels say it is unknown whether the drugs cause these tumors, including medullary thyroid carcinoma, in humans, because the relevance of the rodent findings has not been determined.

The Wegovy label adds that routine calcitonin blood tests or thyroid ultrasounds are of uncertain value for catching MTC early and may lead to unnecessary procedures. Symptoms to report are a lump in the neck, trouble swallowing, shortness of breath or persistent hoarseness.

Thyroid cancer: the human studies

Why the difference? One possible reason is detection bias, which can affect case-control studies more (people on new drugs get more scans and tests, which find small thyroid cancers that would otherwise go unnoticed). The Scandinavian study’s upper confidence limit was consistent with no more than a 31% relative increase. Neither study is long enough to rule out a small long-term risk, which is why the warning stays.

Largest published studies of GLP-1 use and thyroid cancer, read on PubMed Oct 11, 2026.
Study	Design	Result	Grade
Bezin et al., Diabetes Care 2023	French national case-control: 2,562 thyroid cancer cases vs 45,184 controls, type 2 diabetes	1 to 3 years of GLP-1 use linked to more thyroid cancer (HR 1.58, 95% CI 1.27-1.95) and medullary thyroid cancer (HR 1.78, 1.04-3.05)	C
Pasternak et al., BMJ 2024	Cohort in Denmark, Norway and Sweden: 145,410 GLP-1 users vs 291,667 DPP-4 inhibitor users, mean follow-up 3.9 years	No increase in thyroid cancer (HR 0.93, 0.66-1.31); medullary thyroid cancer HR 1.19 (0.37-3.86), too few cases to be precise	C

Pancreatitis: how often it happened

Wegovy (weight trials): acute pancreatitis confirmed in 4 Wegovy-treated patients (0.2 cases per 100 patient-years) versus 1 on placebo (under 0.1).
Ozempic (diabetes trials): 0.3 versus 0.2 cases per 100 patient-years; amylase rose 13% and lipase 22% on average.
Tirzepatide (diabetes trials): 0.23 versus 0.11 patients per 100 years of exposure.
Real world: in a US claims study of people without diabetes using GLP-1s for weight loss, pancreatitis ran 4.6 per 1,000 person-years on semaglutide, higher than on bupropion-naltrexone (Sodhi et al., JAMA 2023).
All three labels say to stop the drug if pancreatitis is suspected. Some trials, such as the 2026 Lancet alcohol trial, excluded people with past pancreatitis, so discuss your history before starting.

Breast, pancreatic and other cancers

In a US electronic-records study of 1,651,452 people with type 2 diabetes followed up to 15 years, GLP-1 users had lower rates than insulin users of 10 of 13 obesity-associated cancers, including pancreatic (HR 0.41), colorectal (0.54) and endometrial cancer (0.74). There was no reduction in postmenopausal breast cancer or thyroid cancer. Compared with metformin users, GLP-1 users had no lower risk of any of the cancers and a higher risk of kidney cancer (HR 1.54). These are observational associations (grade C): they suggest no broad cancer signal, but they do not show that GLP-1s prevent cancer.

FAQ

Does Ozempic cause thyroid cancer?

It is unknown. Semaglutide caused thyroid C-cell tumors in rodents, which is why Ozempic carries a boxed warning. In people, a French study linked 1 to 3 years of GLP-1 use to more thyroid cancer, while a larger Scandinavian cohort of 145,410 users found no increase over about four years.

Who should not take a GLP-1 because of the cancer warning?

The Ozempic, Wegovy, Mounjaro and Zepbound labels say not to use them if you or a family member has had medullary thyroid carcinoma, or if you have multiple endocrine neoplasia syndrome type 2 (MEN 2).

How common is pancreatitis on Wegovy or Zepbound?

Uncommon. In Wegovy’s weight-loss trials, acute pancreatitis was confirmed in 4 treated patients, about 0.2 cases per 100 patient-years, versus 1 on placebo. Tirzepatide trials reported 0.23 versus 0.11 patients per 100 years of exposure. Severe stomach pain that may spread to the back needs urgent care.

Do GLP-1 drugs increase breast cancer risk?

Current data do not show an increase. A US study of 1.65 million people with type 2 diabetes found GLP-1 use was not associated with a change in postmenopausal breast cancer risk compared with insulin. These are observational data, so they cannot rule out small effects.

Should I get my thyroid checked before starting a GLP-1?

Tell your prescriber about any thyroid nodules or family history of thyroid cancer. The Wegovy label says routine calcitonin tests or thyroid ultrasounds are of uncertain value for catching medullary thyroid cancer early and may lead to unnecessary procedures; a neck lump or persistent hoarseness should be checked.

GLP-1 side effects: what the FDA labels say →Every labeled warning in one place.GLP-1 drugs and alcohol →Drinking on a GLP-1, and the alcohol trials.Is compounded semaglutide safe or legal? →What the FDA says in 2026.Cheapest way to get a GLP-1 online →How we compare providers →

Sources

Facts on this page come from the sources below, read Oct 11, 2026. We link only to sellers we have an affiliate relationship with and to government and research sources; other sellers' prices are quoted as plain text.