Several GLP-1 receptor agonists — including Ozempic, Wegovy, Rybelsus, and Mounjaro — carry an FDA Black Box Warning (now known as a boxed warning), the agency’s strongest safety alert. This warning highlights the potential risk of thyroid C-cell tumors, including Medullary Thyroid Carcinoma (MTC). While the full long-term risk to humans is not yet known, the Black Box Warning exists due to concerning findings in animal studies and a lack of long-term human data. This page explains everything you need to know about these warnings and how they may affect GLP-1 drug users.
The FDA issued a boxed warning (formerly known as a Black Box Warning) for Wegovy, Rybelsus and Ozempic. The FDA has required a boxed warning for semaglutide concerning the chance of thyroid C-cell tumors since semaglutide was approved on December 5, 2017.This FDA boxed warning warns patients concerning the link between semaglutide and the likelihood of thyroid c-cell tumors, which specifically includes medullary thyroid carcinoma (MTC). MTC is a very rare type of thyroid cancer that is deadly. Boxed warnings are the most severe form of warning issued by the FDA. Boxed warnings are typically utilized by the FDA when a drugs complications can result in catastrophic harm or even death. These FDA warning were formerly known as “black box warnings.”
GLP-1s –Mounjaro, Zepbound, Victoza and Saxenda– also have boxed warnings which are described below.
What Is a Black Box Warning?
A Black Box Warning (also NOW called a boxed warning) is the highest level of safety caution issued by the FDA.
It appears in a bold black border on drug labels and indicates:
- a risk of serious or life-threatening adverse effects
- the need for careful patient selection
- the importance of monitoring for severe outcomes
For GLP-1 drugs, the warning covers the risk of thyroid C-cell tumors.
Which GLP-1 Drugs Carry a Black Box Warning?
The following drugs include an FDA boxed warning for thyroid C-cell tumors:
Semaglutide-based GLP-1 drugs:
- Ozempic
- Wegovy
- Rybelsus
Tirzepatide-based drugs:
- Mounjaro
- Zepbound
Dulaglutide and Liraglutide based drugs:
- Trulicity (dulaglutide)
- Victoza (liraglutide)
- Saxenda (liraglutide)
Rybelsus, Ozempic and Wegovy all carry the same boxed warning (2025), related to Semaglutide the main ingreient in those drugs, set forth below:
Rybelsus boxed warning (2025):
“WARNING: RISK OF THYROID C-CELL TUMORS
• In rodents, semaglutide causes dose-dependent and treatment-duration-dependent thyroid C-cell
tumors at clinically relevant exposures. It is unknown whether (OZEMPIC OR RYBELSUS OR WEGOVY) causes thyroid C-cell
tumors, including medullary thyroid carcinoma (MTC), in humans as human relevance of
semaglutide-induced rodent thyroid C-cell tumors has not been determined [see Warnings and
Precautions (5.1), Nonclinical Toxicology (13.1)].
• OZEMPIC is contraindicated in patients with a personal or family history of MTC or in patients
with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) [see Contraindications (4)]. Counsel
patients regarding the potential risk for MTC with the use of (OZEMPIC OR RYBELSUS OR WEGOVY) and inform them of
symptoms of thyroid tumors (e.g. a mass in the neck, dysphagia, dyspnea, persistent hoarseness).
Routine monitoring of serum calcitonin or using thyroid ultrasound is of uncertain value for early
detection of MTC in patients treated with (OZEMPIC OR RYBELSUS OR WEGOVY) [see Contraindications (4), Warnings and
Precautions (5.1)].”
Mounjaro and Zepbound have the following boxed warning (2025) (formerly known as a black box warning), related to Tirzepatide the main ingredient in Mounjaro and Zepbound, set forth below:
“WARNING: RISK OF THYROID C-CELL TUMORS
• In both male and female rats, tirzepatide causes dose-dependent and treatment-duration-dependent
thyroid C-cell tumors at clinically relevant exposures. It is unknown whether (MOUNJARO OR ZEPBOUND) causes thyroid
C-cell tumors, including medullary thyroid carcinoma (MTC), in humans as human relevance of tirzepatideinduced rodent thyroid C-cell tumors has not been determined [see Warnings and Precautions (5.1) and Nonclinical Toxicology (13.1)].
• (MOUNJARO OR ZEPBOUND) is contraindicated in patients with a personal or family history of MTC or in patients with
Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) [see Contraindications (4)]. Counsel patients
regarding the potential risk for MTC with the use of (MOUNJARO OR ZEPBOUND) and inform them of symptoms of thyroid
tumors (e.g., a mass in the neck, dysphagia, dyspnea, persistent hoarseness). Routine monitoring of
serum calcitonin or using thyroid ultrasound is of uncertain value for early detection of MTC in patients
treated with (MOUNJARO OR ZEPBOUND) [see Contraindications (4) and Warnings and Precautions (5.1)].”
Trulicity has the following boxed warning (2025) (formerly known as a black box warning), related to dulaglutide the main ingredient in Trulicity, set forth below:
“WARNING: RISK OF THYROID C-CELL TUMORS
• In male and female rats, dulaglutide causes a dose-related and treatment-duration-dependent increase in the
incidence of thyroid C-cell tumors (adenomas and carcinomas) after lifetime exposure. It is unknown whether
TRULICITY causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans as human
relevance of dulaglutide-induced rodent thyroid C-cell tumors has not been determined [see Warnings and
Precautions (5.1), and Nonclinical Toxicology (13.1)].
• TRULICITY is contraindicated in patients with a personal or family history of MTC and in patients with Multiple
Endocrine Neoplasia syndrome type 2 (MEN 2). Counsel patients regarding the potential risk of MTC with use of
TRULICITY and inform them of symptoms of thyroid tumors (e.g., mass in the neck, dysphagia, dyspnea,
persistent hoarseness). Routine monitoring of serum calcitonin or using thyroid ultrasound is of uncertain
value for early detection of MTC in patients treated with TRULICITY [see Contraindications (4) and Warnings
and Precautions (5.1)].
Victoza and Saxenda carry the same boxed warning (2025) (formerly known as a black box warning), related to liraglutide (Victoza, Saxenda) and dulaglutide, (Trulicity), the main ingredients in those drugs, set forth below:
WARNING: RISK OF THYROID C-CELL TUMORS
• Liraglutide causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors at
clinically relevant exposures in both genders of rats and mice. It is unknown whether (SAXENDA OR VICTOZA)
causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans, as the
human relevance of liraglutide-induced rodent thyroid C-cell tumors has not been determined [see
Warnings and Precautions (5.1) and Nonclinical Toxicology (13.1)].
• VICTOZA is contraindicated in patients with a personal or family history of MTC and in patients
with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Counsel patients regarding the
potential risk for MTC with the use of (SAXENDA OR VICTOZA) and inform them of symptoms of thyroid tumors
(e.g., a mass in the neck, dysphagia, dyspnea, persistent hoarseness). Routine monitoring of serum
calcitonin or using thyroid ultrasound is of uncertain value for early detection of MTC in patients
treated with (SAXENDA OR VICTOZA) [see Contraindications (4) and Warnings and Precautions (5.1)].
Why Do GLP-1 Drugs Have a Black Box Warning?
The warning is based on:
- Rodent studies
Rodents given GLP-1 drugs developed:
-
- thyroid C-cell tumors
- medullary thyroid carcinoma
- other C-cell proliferative lesions
- Lack of long-term human studies
There is no reliable 10–20 year data to rule out similar risks in humans.
- Hormonal effects of GLP-1 drugs
GLP-1 receptors are present in thyroid tissue, which suggests a possible biological mechanism.
- Individual case reports
Though rare, some patients have developed thyroid abnormalities while on GLP-1 drugs.
Thyroid Cancer Symptoms to Watch For
Symptoms of thyroid C-cell tumors or MTC include:
- Neck lump or swelling
- Persistent hoarseness
- Difficulty swallowing
- Throat tightness
- Trouble breathing
- Unexplained coughing
- Neck or ear pain
These symptoms should prompt immediate evaluation.
➡️ Thyroid Tumor Risk
Who Should Not Use GLP-1 Drugs?
The boxed warning specifies that GLP-1 drugs should not be used by people who:
- have a personal or family history of MTC
- have MEN-2 (Multiple Endocrine Neoplasia syndrome type 2)
- have unexplained thyroid nodules
- have elevated calcitonin levels
Doctors often require screening questions before prescribing.
Are Humans Actually at Risk for Thyroid Tumors?
The exact risk remains uncertain.
Evidence suggesting possible risk:
- rodent studies showed clear tumors
- GLP-1 receptors exist in human thyroid tissue
- GLP-1 drugs may influence calcitonin production
- isolated human case reports exist
Evidence suggesting lower risk:
- humans have fewer GLP-1 receptors in thyroid tissue
- clinical trials did not show a statistically significant increase
- most cases are anecdotal or isolated
The FDA’s position:
The risk cannot be ruled out.
Therefore, the strongest warning remains in place.
Other Serious GLP-1 Risks (Not Part of the Boxed Warning)
Although the boxed warning only covers thyroid tumors, GLP-1 drugs also carry serious risks such as:
- gastroparesis
- pancreatitis
- intestinal obstruction (bowel obstruction)
- kidney failure
- gallbladder disease
- severe dehydration
What Patients Should Do
If you are taking a GLP-1 drug with a boxed warning:
Monitor for thyroid symptoms
Any neck swelling or difficulty swallowing requires medical evaluation.
Ask your doctor if you have thyroid risk factors
Especially family history of MTC or MEN-2.
Do not stop medication suddenly without medical guidance
Abrupt changes can cause blood sugar issues in diabetic patients.
Request calcitonin levels if concerned
Especially if you have symptoms.
Legal Rights: Thyroid Risks & GLP-1 Lawsuits
Patients who developed thyroid abnormalities, tumors, or other serious injuries while taking GLP-1 drugs may qualify for compensation.
You may have a case if you:
- developed a thyroid tumor
- were diagnosed with medullary thyroid carcinoma
- developed suspicious nodules
- needed surgery or biopsy
- were not properly warned
- suffered other severe GLP-1 complications
Compensation may include:
- medical costs
- surgery and treatment
- long-term cancer care
- lost income
- pain and suffering
- reduced quality of life
➡️ See if you qualify:
👉 GLP-1 Drug Lawsuits
👉 Ozempic Lawsuit
Related Information
- Long-Term GLP-1 Risks
- Severe GLP-1 Reactions
- Common GLP-1 Side Effects
- Thyroid Cancer Overview
- Ozempic Side Effects
- Mounjaro Side Effects
- Wegovy Side Effects
The FDA Black Box Warning for GLP-1 drugs signals the potential risk of thyroid C-cell tumors, including Medullary Thyroid Carcinoma. While human data is still limited, the warning reflects serious safety concerns and the need for monitoring. If you experienced thyroid complications or other severe adverse reactions after using a GLP-1 medication, you may have legal options.