This page summarizes safety information from the FDA-approved prescribing information for tirzepatide (Zepbound, Mounjaro) and semaglutide (Wegovy, Ozempic, Rybelsus) and from FDA communications on compounded GLP-1 products. It is not a substitute for the full prescribing information or for a conversation with your clinician.
Boxed warning: thyroid C-cell tumors
Tirzepatide and semaglutide caused thyroid C-cell tumors in rodents at clinically relevant exposures. It is unknown whether they cause thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans. These medications are contraindicated in people with a personal or family history of MTC or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Report a lump or swelling in the neck, hoarseness, trouble swallowing or shortness of breath to your clinician.
Contraindications
- Personal or family history of MTC or MEN 2.
- Known serious hypersensitivity to the active ingredient or any excipient.
- Pregnancy: discontinue at least two months before a planned pregnancy; not recommended during pregnancy or while breastfeeding.
- Do not use tirzepatide or semaglutide together, or with any other GLP-1 receptor agonist.
Serious adverse reactions in the labeling
- Acute pancreatitis. Discontinue if suspected; do not restart if confirmed.
- Gallbladder disease (cholelithiasis, cholecystitis), more common with rapid weight loss.
- Hypoglycemia, particularly with insulin or sulfonylureas; dose reduction of those agents may be needed.
- Acute kidney injury, usually secondary to dehydration from vomiting or diarrhea.
- Hypersensitivity reactions, including anaphylaxis and angioedema.
- Diabetic retinopathy complications with semaglutide in people with type 2 diabetes and existing retinopathy.
- Severe gastrointestinal disease: not recommended in severe gastroparesis; ileus has been reported post-marketing.
- Suicidal behavior and ideation: monitor for depression or suicidal thoughts; FDA's 2024 review found no evidence of a causal link but the labeling advises monitoring.
- Pulmonary aspiration during anesthesia: delayed gastric emptying can leave food in the stomach; tell your anesthesia team you take a GLP-1 medication.
Common adverse reactions
Nausea, diarrhea, vomiting, constipation, abdominal pain, dyspepsia, injection-site reactions, fatigue, hypersensitivity reactions, belching, hair loss and gastroesophageal reflux. Gastrointestinal effects are most frequent during dose escalation and usually decline over weeks.
Additional risks specific to compounded products
Compounded tirzepatide and semaglutide are not FDA-approved and have not been reviewed by the FDA for safety, effectiveness or quality. The FDA has stated the following concerns:
- Dosing errors. Compounded products are supplied in multi-dose vials requiring the patient to draw up a dose with a syringe. The FDA has received reports of overdoses, some requiring hospitalization, from confusion between units and milliliters or between vial concentrations. Use the dose calculators only as a check on your pharmacist's instructions, never instead of them.
- Salt forms. Some compounders have used semaglutide sodium, semaglutide acetate or tirzepatide salt forms that are not the active ingredient in the approved products and have not been shown to be safe or effective.
- Quality and sterility. Products from unlicensed sources, or from pharmacies that fail to meet sterile compounding standards, may be contaminated, sub- or super-potent, or mislabeled.
- Sublingual and oral compounded forms. No published pharmacokinetic data establish that sublingual or orally disintegrating compounded tirzepatide or semaglutide achieve absorption comparable to injection.
- Post-shortage status. Since the FDA declared the tirzepatide shortage resolved (December 2024) and the semaglutide shortage resolved (February 2025), compounding of essentially a copy of the approved products is not permitted; pharmacies may compound only for individual patients with a documented clinical need for a different formulation.
Before you start
Tell your clinician about all medical conditions, especially thyroid, pancreatic, kidney, gallbladder or gastrointestinal disease, diabetes and its medications, diabetic retinopathy, depression or suicidal thoughts, pregnancy or plans for pregnancy, and every medication you take. Confirm the dispensing pharmacy is licensed in your state.
Reporting adverse events
Report side effects to the FDA at 1-800-FDA-1088 or through MedWatch. In an emergency, call 911.
FDA adverse-event reports for compounded GLP-1s
As of May 31, 2026, the FDA said it had received 990 adverse-event reports associated with compounded semaglutide and more than 730 associated with compounded tirzepatide, up from 215 tirzepatide reports at November 30, 2024. The FDA cautions that reports may be under-counted, because state-licensed pharmacies are not required to file them, and that a report does not by itself establish that the drug caused the event. The most avoidable category is dosing error from multi-dose vials; the dosing checklist addresses it.