GLP-1 thyroid warning and contraindications: what the labels say

Short answer: every US label for Ozempic, Wegovy, Rybelsus, Mounjaro, Zepbound, Saxenda, Victoza and Trulicity has a boxed warning for thyroid C-cell tumors, based on rodent studies. All of them are contraindicated if you or a family member has had medullary thyroid carcinoma (MTC), or you have MEN 2. The Canadian monographs carry the same warning in a "Serious Warnings and Precautions Box", and all eight add pregnancy as a contraindication.

On this page: The thyroid warning · Contraindications, US vs Canada · Canadian box compared · Warnings by label · NAION in Canada · Symptoms to report · What to tell your prescriber

The thyroid C-cell tumor warning

The US boxed warning, "Warning: risk of thyroid C-cell tumors", says that in rodents the drug causes dose-dependent and treatment-duration-dependent thyroid C-cell tumors at clinically relevant exposures. It is unknown whether the drug causes these tumors, including MTC, in humans, because the human relevance of the rodent tumors has not been determined. For semaglutide and tirzepatide the tumors were seen in rats (and mice for semaglutide); the liraglutide labels note that malignant C-cell carcinomas were found in rats and mice.

The semaglutide labels add that cases of MTC have been reported after marketing in people treated with liraglutide, another GLP-1 receptor agonist, and that these reports are insufficient to establish or exclude a causal link.

In Canada, all eight product monographs put the same risk in section 3, the Serious Warnings and Precautions Box. The Ozempic monograph says human relevance "could not be ruled out by clinical or nonclinical studies", and the Ozempic and Mounjaro monographs say it is unknown whether monitoring with serum calcitonin or thyroid ultrasound will mitigate human risk. The US labels say routine calcitonin or ultrasound monitoring is of uncertain value for early detection of MTC.

Who should not take them: contraindications, US vs Canada

"Contraindicated" means the label says the drug must not be used in that situation. MEN 2 is Multiple Endocrine Neoplasia syndrome type 2, an inherited condition linked to MTC.

The biggest US vs Canada difference is pregnancy. Every Canadian monograph above lists pregnancy in section 2, and all but Zepbound also list breastfeeding. The US labels treat pregnancy and lactation in section 8 (Use in specific populations) rather than as a contraindication.

For more on the pregnancy wording and the 2-month and 1-month stop rules, see GLP-1s, pregnancy and breastfeeding.

The Canadian Serious Warnings box, monograph by monograph

Each Canadian monograph has the thyroid C-cell tumour warning in section 3. The core message is the same, but the wording differs in three places: which rodents were studied, how the monograph describes human relevance, and what it says about calcitonin or thyroid ultrasound monitoring. Dates are the monograph authorization or revision dates on the versions we read.

Every box ends with the same instruction: the drug is contraindicated with a personal or family history of MTC or with MEN 2, and patients should be counselled about the risk and symptoms of thyroid tumours. The Saxenda and Victoza boxes are the only ones that say routine monitoring in trials "may have increased the number of unnecessary thyroid surgeries".

Warnings and precautions, label by label (US)

Section 5 of each US label lists its warnings and precautions. Most are shared across the class; a few appear on only some labels. This table is built from the highlights of the eight current US labels on DailyMed.

What a few of these mean in plain words

• Pancreatitis: the labels say to stop the drug if pancreatitis is suspected. The symptom they describe is persistent or severe abdominal pain, sometimes spreading to the back, with or without nausea or vomiting. Our pancreatitis and gallbladder guide lists the trial rates for each drug.
• Hypoglycemia: low blood sugar is mainly a risk when a GLP-1 is combined with insulin or a sulfonylurea, and the labels say the dose of those other drugs may need to be reduced. That decision belongs to your prescriber.
• Kidney injury from dehydration: vomiting, diarrhea or not drinking enough can lead to fluid loss. The labels ask prescribers to monitor kidney function in people with these side effects.
• Gallbladder disease: gallstones and gallbladder inflammation were reported in trials; the labels call for gallbladder studies if suspected.
• Aspiration under anesthesia: because these drugs slow stomach emptying, food may remain in the stomach during sedation. Tell anyone doing a procedure or surgery that you take a GLP-1. Full label-by-label detail is in our GLP-1 aspiration risk under anesthesia guide.

Vision loss (NAION): a Canadian monograph warning

Non-arteritic anterior ischemic optic neuropathy (NAION) is damage to the optic nerve from reduced blood flow, which can cause sudden vision loss in one eye. Four Canadian monographs now list it under section 7, Warnings and Precautions. Each says there is no identified time interval for when NAION may develop after starting treatment, that anyone reporting a sudden loss of vision (including partial loss) should be urgently referred for an eye examination, and that treatment should be stopped if NAION is confirmed.

If your vision changes suddenly while on any GLP-1, contact a healthcare provider right away. Logging the date in a GLP-1 tracker such as Glidedose helps you report when it started.

Thyroid symptoms the labels list

The US labels ask prescribers to tell patients about possible symptoms of thyroid tumors:

• a lump or mass in the neck
• trouble swallowing (dysphagia)
• shortness of breath (dyspnea)
• hoarseness that does not go away

If you notice any of these, contact your healthcare provider. A GLP-1 tracker such as Glidedose lets you log symptoms with a date, which makes it easier to describe when something started.

What to tell your prescriber before starting

• Any personal or family history of medullary thyroid carcinoma, or a diagnosis of MEN 2.
• Any past allergic reaction to a GLP-1 or its ingredients.
• A history of pancreatitis, gallbladder problems, kidney problems, severe gastroparesis or diabetic retinopathy.
• Whether you take insulin or a sulfonylurea.
• Whether you are pregnant, planning a pregnancy or breastfeeding.
• Any planned surgery or procedure that needs anesthesia or sedation.
• Mood changes or psychiatric history — see the suicidal ideation and depression warning for US vs Canada label status.

Sources

• Ozempic prescribing information, boxed warning and sections 4 and 5 (DailyMed, US)
• Wegovy prescribing information, boxed warning and sections 4 and 5 (DailyMed, US)
• Rybelsus and Ozempic tablets prescribing information (DailyMed, US)
• Mounjaro prescribing information (DailyMed, US)
• Zepbound prescribing information (DailyMed, US)
• Saxenda prescribing information (DailyMed, US)
• Victoza prescribing information (DailyMed, US)
• Trulicity prescribing information (DailyMed, US)
• Ozempic product monograph, sections 2, 3 and 7 (Novo Nordisk Canada)
• Wegovy product monograph, sections 2 and 3 (Novo Nordisk Canada)
• Mounjaro product monograph, sections 2, 3 and 7 (Eli Lilly Canada)
• Zepbound product monograph, sections 2, 3 and 7 (Eli Lilly Canada)
• Trulicity product monograph, sections 2 and 3 (Eli Lilly Canada)
• Rybelsus product monograph, sections 2, 3 and 7 (Novo Nordisk Canada)
• Saxenda product monograph, sections 2 and 3 (Novo Nordisk Canada)
• Victoza product monograph, sections 2 and 3 (Novo Nordisk Canada)

This page summarizes official product labels as general information. It is not medical advice. Do not start, stop or change any medication without talking to your prescriber. Labels are updated; check the current version for your product.

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