The most common side effects of GLP-1 medications are nausea, vomiting, diarrhea, constipation, abdominal pain, bloating and indigestion. These effects are often strongest when treatment starts or the dose increases.
In adult weight-management trials for Wegovy, gastrointestinal side effects occurred in 73% of participants receiving the medication, compared with 47% receiving placebo. The 2026 FDA prescribing information reports nausea in 44% of Wegovy-treated participants, diarrhea in 30% and vomiting in 25%. These figures do not predict the risk for every GLP-1 medication because trial populations, doses and treatment schedules differ.
Semaglutide products such as Ozempic and Wegovy, and tirzepatide products such as Mounjaro and Zepbound, can cause similar digestive symptoms. The exact risks vary by medication and dose.
Common GLP-1 Side Effects
| Side effect | What it may feel like | What to know |
|---|---|---|
| Nausea | Queasiness or reduced appetite | Often occurs during dose increases |
| Vomiting | Feeling sick or being unable to keep food down | Persistent vomiting can cause dehydration |
| Diarrhea | Loose or frequent stools | May contribute to dehydration |
| Constipation | Fewer or harder bowel movements | Can become severe in some people |
| Abdominal pain | Stomach discomfort or cramping | Severe or persistent pain needs medical assessment |
| Bloating and indigestion | Fullness, burping, reflux or gas | GLP-1 medicines slow stomach emptying |
| Headache, dizziness or fatigue | Feeling light-headed, tired or unwell | Dizziness can worsen if vomiting or diarrhea causes fluid loss |
For Zepbound, FDA prescribing information reports gastrointestinal side effects in 56% of participants receiving each studied dose, compared with 30% receiving placebo. Most nausea, vomiting and diarrhea occurred during dose escalation and decreased over time.
Which GLP-1 Side Effects Require Urgent Medical Attention?
Contact a healthcare professional promptly, or seek urgent care, if you have:
- Severe or persistent abdominal pain, especially if it spreads to the back or occurs with vomiting. This may indicate pancreatitis.
- Repeated vomiting or diarrhea, inability to keep fluids down, fainting or very little urination. These symptoms can cause dehydration and acute kidney injury.
- Severe constipation, abdominal swelling or inability to pass stool or gas, which may indicate a serious gastrointestinal problem.
- Pain in the upper right abdomen, fever or yellowing of the skin or eyes, which may indicate gallbladder disease.
- Swelling of the face, lips, tongue or throat, hives or difficulty breathing, which may indicate a serious allergic reaction.
- Shakiness, sweating, confusion, weakness or fainting, particularly if you take the GLP-1 medicine with insulin or a sulfonylurea. These can be symptoms of low blood sugar.
FDA prescribing information for semaglutide and tirzepatide identifies pancreatitis, gallbladder disease, acute kidney injury caused by dehydration, severe gastrointestinal reactions and serious hypersensitivity reactions as important risks.
Less Common but Important Risks
Low Blood Sugar
GLP-1 medicines do not usually cause severe hypoglycemia when used alone. The risk increases when they are combined with insulin or sulfonylurea medicines, such as glipizide or glyburide. A prescriber may need to adjust the dose of the other diabetes medication.
Gallstones and Gallbladder Inflammation
Gallstones and cholecystitis, or inflammation of the gallbladder, have been reported with GLP-1 medicines. Rapid weight loss may also contribute to gallbladder problems. Seek medical advice for persistent upper-abdominal pain, fever or jaundice.
Worsening Diabetic Retinopathy
Semaglutide labeling includes a warning about diabetic retinopathy complications. People with existing diabetic eye disease should be monitored, particularly when blood glucose improves quickly. Report new or worsening blurred vision, floaters or vision loss.
Delayed Stomach Emptying
GLP-1 medicines slow gastric emptying. This can worsen symptoms in people with severe gastroparesis and may affect the absorption of some oral medicines. Tell the prescribing clinician if you have significant early fullness, recurrent vomiting or a diagnosed stomach-emptying disorder.
Aspiration During Anesthesia or Deep Sedation
Rare cases of pulmonary aspiration have been reported in people taking GLP-1 medicines who underwent general anesthesia or deep sedation. Some had residual stomach contents despite following fasting instructions. Tell the surgeon, anesthesiologist or procedural clinician that you take a GLP-1 medicine before any planned procedure.
Thyroid C-Cell Tumor Warning
Semaglutide and tirzepatide carry a boxed warning because thyroid C-cell tumors occurred in rodents. It is unknown whether these medicines cause thyroid C-cell tumors in humans.
These medicines are contraindicated in people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. Report a neck lump, persistent hoarseness, difficulty swallowing or difficulty breathing.
How to Reduce GLP-1 Side Effects
- Follow the prescribed dose-escalation schedule. Do not increase the dose faster than instructed.
- Eat smaller meals and stop when you feel full.
- Drink enough fluids, especially if you have diarrhea or vomiting.
- Contact your prescriber if symptoms persist. Do not stop or restart treatment on your own.
- Review other medicines that affect blood sugar, digestion or blood pressure.
- Use extra caution with compounded GLP-1 products. FDA reports that dosing errors involving compounded semaglutide have caused severe nausea, vomiting, abdominal pain, dehydration, pancreatitis and gallstones. Some patients required hospitalization.