GLP-1 side effects from the FDA labels: common digestive effects by brand, serious risks, the thyroid boxed warning, muscle and hair loss, and when to call a doctor.
Fact-checked against FDA labels and official sources; not yet reviewed by a licensed clinician. This page is education, not medical advice. Talk to your doctor before starting, stopping or changing any treatment.
Key takeaways
- Digestive side effects are the most common with GLP-1 medicines: on Wegovy injection, nausea was reported by 44% versus 16% on placebo, mostly during dose increases.[1]
- Serious risks on the labels include pancreatitis, gallbladder disease, kidney injury from dehydration, low blood sugar with insulin or sulfonylureas, and aspiration during anesthesia.[1]
- Injectable GLP-1 medicines carry a boxed warning about thyroid C-cell tumors seen in rodents and are not for people with a history of MTC or MEN 2.[2]
- In January 2026 the FDA found no increased risk of suicidal thoughts with GLP-1 receptor agonists and asked makers to remove that warning.[6]
- Lean mass made up anywhere from about 15% or less to 40-60% of weight lost across GLP-1 studies, a 2024 review found.[7]
In short: The most common side effects of GLP-1 medicines such as Wegovy, Zepbound, Ozempic and Mounjaro are digestive: nausea, diarrhea, vomiting and constipation, mostly while the dose is being increased. Serious problems are less common but important to know: pancreatitis, gallbladder disease, low blood sugar when combined with some diabetes medicines, kidney injury from dehydration, and a boxed warning about thyroid tumors seen in rodents. This guide summarizes what the FDA labels say (checked on 2026-10-06) and when to call a doctor.
“GLP-1” here covers the medicines that act on the GLP-1 receptor, including semaglutide (Wegovy, Ozempic, Rybelsus), tirzepatide (Zepbound, Mounjaro), which also acts on the GIP receptor, and newer pills such as Foundayo. Each has its own label, and the numbers below come from those labels. This is general information, not personal medical advice: your prescriber knows your health history and decides how to manage any side effect.
The common ones: stomach and digestion
Side effects in four numbers
- 73% vs 47%adults with at least one digestive side effect on Wegovy 2.4 mg vs placeboWegovy label, section 6.1
- 4.1% vs 0.9%had a severe digestive reaction on Wegovy vs placeboWegovy label, section 6.1
- 56% vs 30%adults with a digestive side effect on Zepbound (any dose) vs placeboZepbound label, section 6.1
- Mostnausea, vomiting and diarrhea happened during dose increases and eased over time, per the labelsZepbound label, section 6.1
Checked on October 6, 2026
GLP-1 medicines slow how quickly the stomach empties and act on appetite signals, which is part of how they work and also why the gut feels it. The Wegovy label reports that in its adult weight trials, 73% of people on the injection and 47% on placebo had at least one digestive side effect, and that these reactions were most often reported during dose escalation. Severe digestive reactions were reported in 4.1% on Wegovy injection versus 0.9% on placebo.
| Side effect | Wegovy 2.4 mg (vs placebo) | Zepbound 5 to 15 mg (vs placebo) | Ozempic 0.5 to 1 mg (vs placebo) | Foundayo, highest strength (vs placebo) |
|---|---|---|---|---|
| Nausea | 44% (16%) | 25-29% (8%) | 15.8-20.3% (6.1%) | 35% (10%) |
| Diarrhea | 30% (16%) | 19-23% (8%) | 8.5-8.8% (1.9%) | 25% (11%) |
| Vomiting | 24% (6%) | 8-13% (2%) | 5.0-9.2% (2.3%) | 24% (4%) |
| Constipation | 24% (11%) | 11-17% (5%) | 3.1-5.0% (1.5%) | 24% (9%) |
| Abdominal pain | 20% (10%) | 9-10% (5%) | 5.7-7.3% (4.6%) | 14% (7%) |
Labels also list indigestion, bloating, burping, gas, reflux, headache, fatigue and dizziness. The labels describe starting at a low dose and increasing it step by step to reduce these effects; how fast to go, and whether to pause or step back, is your prescriber’s decision. Practical habits that people with GLP-1 nausea often discuss with their care team include smaller meals, eating slowly, stopping when full, limiting greasy or very rich food and drinking enough fluids. Our guide to eating on a GLP-1 covers food choices in more detail.
Most people continue treatment despite these effects, but some stop: in Wegovy’s adult weight trials, 6.8% stopped because of side effects compared with 3.2% on placebo.
| Item | Medicine | Placebo |
|---|---|---|
| Wegovy 2.4 mg injection | 44% | 16% |
| Wegovy 7.2 mg (HD) | 39% | 13% |
| Zepbound 15 mg | 28% | 8% |
| Foundayo 17.2 mg pill | 35% | 10% |
| Saxenda 3 mg daily injection | 39.3% | 13.8% |
Separate trials; read each pair on its own. Saxenda is liraglutide, an older daily GLP-1.
Source: Wegovy, Zepbound, Foundayo and Saxenda prescribing information, adverse-reaction tables (DailyMed) (checked on October 6, 2026)
| Item | Medicine | Placebo |
|---|---|---|
| Wegovy 2.4 mg | 6.8% | 3.2% |
| Zepbound 15 mg | 6.7% | 3.4% |
| Foundayo 17.2 mg | 10% | 3% |
| Saxenda 3 mg | 9.8% | 4.3% |
| Wegovy 25 mg tablets | 6.9% | 5.9% |
Source: Prescribing information for each medicine, section 6.1 (DailyMed) (checked on October 6, 2026)
| Item | Medicine | Placebo |
|---|---|---|
| Wegovy 2.4 mg | 73% | 47% |
| Zepbound (each dose) | 56% | 30% |
| Foundayo 17.2 mg | 69% | 37% |
| Ozempic 1 mg (diabetes) | 36.4% | 15.3% |
| Mounjaro 15 mg (diabetes) | 43.6% | 20.4% |
Source: Wegovy, Zepbound, Foundayo, Ozempic and Mounjaro prescribing information, section 6.1 (DailyMed) (checked on October 6, 2026)
When digestive side effects usually show up, according to the labels
- First weeksA low starting dose is used precisely because nausea is most likely early on.
- Each dose increaseNausea, vomiting and diarrhea cluster around step-ups; the labels let prescribers slow down or delay a step.
- After the dose is stableThe labels report that these effects decreased over time for most people.
- Any timeSevere, lasting vomiting or diarrhea can cause dehydration and kidney injury; call the prescriber.
Serious side effects listed on the labels
- Acute pancreatitis. Inflammation of the pancreas, including rare severe and fatal cases, has been seen with GLP-1 receptor agonists. The Wegovy label names the warning sign: persistent or severe abdominal pain, sometimes spreading to the back, with or without nausea or vomiting. If pancreatitis is suspected, the label says to stop the medicine.
- Gallbladder disease. Gallstones and gallbladder inflammation happen more often on these medicines. In Wegovy’s adult trials, gallstones were reported in 1.6% on the injection versus 0.7% on placebo; in Zepbound’s trials, gallbladder inflammation was reported in 0.7% versus 0.2%. The Zepbound label notes that gallbladder events were associated with weight reduction.
- Low blood sugar. The risk rises when a GLP-1 medicine is combined with insulin or a sulfonylurea; prescribers may lower those medicines.
- Kidney injury. Severe vomiting or diarrhea can cause dehydration, which can harm the kidneys. Keeping fluids up matters.
- Severe gastrointestinal reactions. Post-marketing reports include ileus, intestinal blockage and severe constipation.
- Allergic reactions, including anaphylaxis and swelling of the face or throat.
- Diabetic eye disease. People with type 2 diabetes and existing retinopathy may see complications, which the labels ask prescribers to monitor.
- Aspiration during anesthesia. Because the stomach empties more slowly, stomach contents have been inhaled during surgery or deep sedation. Tell every surgical or endoscopy team that you take a GLP-1 medicine.
How often do the serious ones happen? The labels give the numbers below from their trials. They are small percentages, but across millions of users they add up, which is why the warning signs matter.
| Item | Medicine | Placebo |
|---|---|---|
| Wegovy 2.4 mg injection | 1.6% | 0.7% |
| Wegovy 25 mg tablets | 2.5% | 1% |
| Wegovy injection, teens | 3.8% | 0% |
| Zepbound | 1.1% | 1% |
| Foundayo | 1% | 0.7% |
Fast weight loss itself raises gallstone risk.
Source: Wegovy, Zepbound and Foundayo prescribing information, section 6.1 (DailyMed) (checked on October 6, 2026)
- Pancreatitis (per 100 patient-years): Wegovy 0.2 versus under 0.1; Zepbound weight trials 0.14 versus 0.15; Foundayo 0.14 versus 0.04.
- Kidney injury: Wegovy 0.4 versus 0.2 cases per 100 patient-years; Zepbound 0.5% versus 0.2%; Foundayo 0.2% versus 0.05%. Most cases followed vomiting, diarrhea or dehydration.
- Low blood pressure: Wegovy 1.3% versus 0.4%; Zepbound 1.6% versus 0.1%; Foundayo 2% versus 0.5%, more often with blood-pressure medicines.
- Low blood sugar in type 2 diabetes: Wegovy 6.2% versus 2.5%; Zepbound 4.2% versus 1.3%; Foundayo 2% versus 0.2% (7% with a sulfonylurea).
- Diabetic eye complications: 3.0% versus 1.8% with semaglutide in SUSTAIN-6, mostly in people with existing retinopathy.
Pills compared with injections
Taking a GLP-1 medicine by mouth does not avoid the digestive side effects, because they come from the way the medicine acts on the gut and brain, not from the needle. The Wegovy label reports severe digestive reactions in 2% of people on Wegovy tablets versus 0% on placebo, and gallstones in 2.5% versus 1%. In the Foundayo trials summarized on its label, nausea, constipation, diarrhea and vomiting were again the most common effects at the highest strength. Pills have their own rules: the Wegovy pill must be taken on an empty stomach with a small amount of water and a wait before eating, while Foundayo can be taken with or without food. Our weight-loss pills hub compares the options.
The labels also list a faster resting heart rate as a warning: tell your prescriber if you notice palpitations or a racing heartbeat while at rest.
The thyroid boxed warning
The injectable GLP-1 medicines for weight carry a boxed warning, the FDA’s most prominent kind. In mice and rats, semaglutide caused thyroid C-cell tumors, and tirzepatide caused them in rats; it is not known whether these medicines cause such tumors, including medullary thyroid carcinoma (MTC), in humans. For that reason the labels say they should not be used by people with a personal or family history of MTC or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). The labels ask people to report a lump or swelling in the neck, trouble swallowing, hoarseness or shortness of breath. The Foundayo label notes that orforglipron is not active in rats or mice and did not produce tumors in rodents, but it carries the class warning as well.
Mood and mental health: what changed in 2026
Earlier labels for Saxenda, Wegovy and Zepbound carried a warning to watch for suicidal thoughts. On January 13, 2026, after reviewing 91 placebo-controlled trials with 107,910 patients, health-care claims from more than 2.2 million people and published studies, the FDA said it found no increased risk of suicidal thoughts or behavior with GLP-1 receptor agonists and asked the makers to remove that warning. The FDA still asks people to tell their health care professional about new or worsening depression, suicidal thoughts or unusual mood changes. In a crisis, call or text 988.
Muscle loss, hair loss and other changes
Lean mass. Any large weight loss includes some lean tissue, not only fat. A 2024 review of GLP-1-based therapies found that studies vary widely, with lean mass making up anywhere from about 15% or less to 40% to 60% of the weight lost, and that the muscle changes may be partly adaptive. How much this matters for strength and function is still being studied. Protein intake and strength training are the usual ways people work to protect muscle; see muscle loss on GLP-1s, our strength training guide and the protein calculator.
Hair loss. Wegovy’s label lists hair loss in 3% versus 1% on placebo. The Zepbound label reports it was linked with weight reduction and was more frequent in women (7.1%) than men (0.5%).
Face and skin. Changes in the face after fast weight loss are often called “Ozempic face.” They reflect fat loss, not a separate drug effect; see Ozempic face and loose skin after weight loss.
Other medicines and birth control. Slower stomach emptying can change how other pills are absorbed. The Zepbound, Mounjaro and Foundayo labels advise people on oral contraceptives to use a non-oral method or add a barrier method for a period after starting and after each dose increase. Ask your prescriber or pharmacist to check your other medicines.
Pregnancy and breastfeeding
The Wegovy and Zepbound labels state that weight loss offers no benefit during pregnancy and may cause harm to the fetus, and that these medicines should be stopped when a pregnancy is recognized. The Ozempic label advises stopping at least two months before a planned pregnancy. Anyone who is pregnant, planning a pregnancy or breastfeeding should talk with their clinician before starting or continuing a GLP-1 medicine.
When to call a doctor
- Get urgent help for severe abdominal pain that does not go away (with or without vomiting), or signs of a serious allergic reaction such as swelling of the face, lips, tongue or throat, problems breathing or swallowing, a very rapid heartbeat or fainting. The Medication Guide says to stop the medicine and get medical help right away for an allergic reaction.
- Call your prescriber soon for vomiting or diarrhea that keeps you from drinking enough, pain in the upper stomach, fever, yellowing of the skin or eyes or clay-colored stools (possible gallbladder problems), a lump or swelling in the neck, hoarseness or trouble swallowing, symptoms of low blood sugar if you also take diabetes medicines, vision changes if you have type 2 diabetes, or a racing heartbeat at rest.
- Before any procedure with anesthesia or sedation, tell the team you take a GLP-1 medicine.
Side effects can be reported to the FDA’s MedWatch program online or at 1-800-332-1088.
Side effects brand by brand
Each medication page has its label details: Wegovy, Zepbound, Ozempic, Mounjaro, the Wegovy pill and Foundayo. Dedicated pages cover Wegovy side effects, Zepbound side effects and Ozempic side effects. Compounded products carry the same ingredient risks plus the dosing and quality problems the FDA has reported; see compounded GLP-1s. For the bigger picture, return to the weight-loss injections hub or the GLP-1 guide.
Before and during treatment: a checklist
Practical steps to discuss with your care team
- Before startingShare any history of pancreatitis, gallstones, kidney disease, diabetic eye disease, thyroid cancer or MEN 2 in the family.
- MedicinesList insulin, sulfonylureas, blood-pressure pills, birth-control pills, thyroid medicine and anything taken by mouth.
- FluidsThe labels ask people to avoid fluid loss; call if vomiting or diarrhea will not stop.
- ProceduresTell any surgeon, dentist doing sedation or endoscopy team that you take a GLP-1 medicine.
- ReportNote new symptoms and report serious ones to your prescriber and to FDA MedWatch.
InstaTuck is an information site; we do not sell or prescribe any of these medicines. If you are considering one, a licensed clinician who reviews your history is the right first step, and our obesity medicine guide explains what to look for. For eating well while appetite is low, see eating on a GLP-1; for keeping strength, muscle loss on GLP-1s.
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- Which side effects should make me call you, and which can I manage at home?
- If nausea is hard to handle, can we slow the dose increases?
- Do any of my other medicines, including diabetes medicines or birth control pills, need to change?
- Do I have any history, such as pancreatitis, gallstones or thyroid conditions, that matters here?
- How much protein and what kind of exercise should I aim for to protect muscle?
Frequently asked questions
How long does GLP-1 nausea last?
The labels report that digestive side effects were most frequent during dose escalation. For many people they ease once the dose is stable, but this varies. If nausea or vomiting keeps you from eating or drinking normally, contact your prescriber.
Are the side effects of Zepbound and Wegovy different?
They are similar in kind: mostly nausea, diarrhea, vomiting and constipation. The labels report different rates, but they come from different trials, so they cannot be compared directly.
Do GLP-1 drugs cause thyroid cancer?
Semaglutide and tirzepatide caused thyroid C-cell tumors in rodents. It is not known whether they cause these tumors in humans. The labels say people with a personal or family history of medullary thyroid carcinoma or MEN 2 should not use them.
Do GLP-1 medicines cause muscle loss?
Part of any large weight loss is lean mass. Studies of GLP-1-based therapies report a wide range. Eating enough protein and doing strength training are the usual ways to help protect muscle; ask your care team for a plan.
Should I stop my GLP-1 before surgery?
Tell your surgical or endoscopy team well in advance. The labels warn about aspiration during anesthesia or deep sedation, and the team will tell you what to do.
How long does GLP-1 nausea last?
The labels report that nausea, vomiting and diarrhea occurred mostly during dose escalation and decreased over time. How long it lasts varies; if it is severe or stops you drinking fluids, contact your prescriber.
Which GLP-1 has the fewest side effects?
The labels cannot answer that directly, because each drug was tested in separate trials with different placebo rates. In their own trials, nausea ranged from 28% (Zepbound 15 mg) to 44% (Wegovy 2.4 mg), with placebo rates from 8% to 16%.
Do GLP-1 pills cause fewer side effects than injections?
Not necessarily. Foundayo reported nausea in 35% at the highest dose versus 10% on placebo, and the Wegovy tablet label says its common side effects were similar to the injection.
Can GLP-1 medicines cause gallstones?
Yes. Gallstones were reported in about 1% to 2.5% of adults in the weight trials, slightly more than on placebo, and in 3.8% of teens on Wegovy. Fast weight loss itself raises the risk.
References
- WEGOVY (semaglutide) injection and tablets: prescribing information. Novo Nordisk, via DailyMed, 2026. (accessed October 7, 2026) Drug label
- ZEPBOUND (tirzepatide) injection: prescribing information. Eli Lilly and Company, via DailyMed, 2026. (accessed October 7, 2026) Drug label
- OZEMPIC (semaglutide) injection: prescribing information. Novo Nordisk, via DailyMed, 2026. (accessed October 7, 2026) Drug label
- MOUNJARO (tirzepatide) injection: prescribing information. Eli Lilly and Company, via DailyMed, 2026. (accessed October 7, 2026) Drug label
- FOUNDAYO (orforglipron) tablets: prescribing information. Eli Lilly and Company, via DailyMed, 2026. (accessed October 7, 2026) Drug label
- FDA requests removal of suicidal behavior and ideation warning from GLP-1 receptor agonist medications. U.S. Food and Drug Administration, 2026. (accessed October 6, 2026) Government page
- Neeland IJ, Linge J, Birkenfeld AL. Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies. Diabetes, Obesity and Metabolism, 2024. doi:10.1111/dom.15728 · PMID 38937282 (accessed October 6, 2026) Review
- SAXENDA (liraglutide) injection: prescribing information. Novo Nordisk, via DailyMed, 2026. (accessed October 6, 2026) Drug label
Facts checked on October 6, 2026
Educational information, not medical advice. Talk with a qualified healthcare professional about your own situation. In an emergency call 911.