GLP-1 Side Effects: What Every GLP-1 Drug Label Warns About

GLP-1 side effects are mostly digestive. In the U.S. prescribing information for every approved GLP-1 medicine, nausea, diarrhea, vomiting, constipation and stomach pain are the most common, and they happen most often while the medicine is being stepped up to its maintenance strength. The labels also share a set of class warnings: a boxed warning about thyroid C-cell tumors seen in rodent studies, pancreatitis, gallbladder disease, low blood sugar when combined with insulin or a sulfonylurea, kidney injury from dehydration, severe digestive reactions, allergic reactions and a risk of inhaling stomach contents during anesthesia. This guide compares the side effects of GLP-1 drugs label by label.

Peptide Labs does not sell GLP-1 medicines or any prescription drug. This article is general information, not medical advice. For how these drugs work, see what GLP-1 is.

Common GLP-1 side effects, drug by drug

The table lists the most frequent side effects in each drug’s current U.S. label. Percentages come from each label’s placebo-controlled trials, and ranges span the maintenance strengths. The trials enrolled different people for different lengths of time, so the numbers are context, not a head-to-head ranking.

Two patterns stand out. Weight-management versions, used at higher strengths, report more digestive effects than diabetes versions of the same molecule, as Wegovy and Ozempic show. And the labels say most nausea, vomiting and diarrhea occurred while the medicine was being stepped up, easing over time. A 2014 review in the Review of Diabetic Studies reached the same conclusion for the older drugs in the class: digestive symptoms, mainly nausea, were the most common adverse effects.

How often people stop because of side effects

In weight-management trials, the share who stopped because of an adverse reaction was 6.8% on Wegovy (3.2% on placebo), 4.8% to 6.7% on Zepbound (3.4%), 9.8% on Saxenda (4.3%) and 8% on Foundayo (3%). Digestive reactions of any severity affected 73% of adults on Wegovy versus 47% on placebo, and 56% on Zepbound versus 30%. Vomiting and diarrhea can cause dehydration and kidney injury.

GLP-1 agonist side effects: the shared class warnings

Because the drugs act on the same receptor, the serious GLP-1 agonist side effects are largely shared. All seven labels in the table include:

• Boxed warning on thyroid C-cell tumors, based on rodent findings in the class; whether they occur in humans is unknown. The drugs are not for people with a personal or family history of medullary thyroid carcinoma or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
• Pancreatitis: confirmed in 4 people on Wegovy versus 1 on placebo in its adult weight trials; severe, persistent stomach pain needs prompt care.
• Gallbladder disease, including gallstones. Wegovy’s label says substantial or rapid weight loss can raise the risk, and that the excess risk remained after accounting for weight lost.
• Low blood sugar when combined with insulin or a sulfonylurea. In Zepbound’s diabetes trial, 10.3% of people also taking a sulfonylurea had low blood sugar.
• Acute kidney injury from dehydration after vomiting or diarrhea.
• Severe digestive reactions; most of these labels say the drug is not recommended in severe gastroparesis.
• Serious allergic reactions and aspiration during anesthesia or deep sedation, covered below.

Other warnings appear on only part of the class, as the next table shows. Trulicity (dulaglutide), a weekly diabetes injection, carries the same boxed thyroid warning.

In the SUSTAIN-6 trial of semaglutide in type 2 diabetes, diabetic eye complications were more frequent than on placebo; the labels link temporary worsening to rapid improvement in blood sugar. Tirzepatide and Foundayo can make birth control pills less reliable for a period after starting and after each step-up, so their labels advise a non-oral or backup method. Reports after approval also include bowel obstruction, ileus and severe constipation.

Side effects of GLP-1 drugs around surgery and anesthesia

GLP-1 drugs slow stomach emptying, so food can stay in the stomach longer. The labels warn about rare reports of pulmonary aspiration, meaning stomach contents entering the lungs, during general anesthesia or deep sedation, and the Saxenda label says available data are insufficient to recommend how to reduce that risk. On October 29, 2024, the American Society of Anesthesiologists and four other medical societies issued guidance that most patients can continue GLP-1 drugs before elective surgery. People at highest risk, such as those early in the step-up period, on higher strengths, or with nausea, vomiting or constipation, may be asked to follow a liquid-only diet for 24 hours beforehand. Tell your care team well ahead of any procedure, and do not stop the drug on your own.

GLP-1 weight loss side effects: muscle, hair, face and gallstones

Some GLP-1 weight loss side effects reflect rapid weight loss rather than the drug itself.

• Muscle and lean mass: the Wegovy and Zepbound labels state that the drugs lower weight with greater fat loss than lean mass loss, but lean mass still falls. A 2026 meta-analysis of 7 randomized trials with 821 people found an average lean mass loss of 1.74 kg, while lean mass as a share of body weight rose. The authors advised pairing drug therapy with nutrition and exercise.
• Hair shedding: listed on the Wegovy (3% vs 1%) and Zepbound (4% to 5% vs 1%) labels, far more often in women. See our guide to hair loss on GLP-1 drugs.
• Facial volume loss: not listed on any U.S. label; the evidence links it to the amount of weight lost. See what “Ozempic face” means.
• Gallstones: rapid weight loss raises the risk, as noted above.

What changed on the labels: suicidal thoughts and NAION

On January 13, 2026, the FDA asked for the suicidal behavior and ideation warning to be removed from Saxenda, Wegovy and Zepbound after a review of 91 placebo-controlled trials and data on more than 2.2 million new users found no increased risk. The FDA still advises telling a health professional about new or worsening depression or mood changes.

NAION (non-arteritic anterior ischemic optic neuropathy) is a rare optic nerve condition that can cause sudden vision loss. The European Medicines Agency’s safety committee concluded in June 2025 that it is a very rare side effect of semaglutide, affecting up to 1 in 10,000 people, and the UK’s MHRA issued a safety update in February 2026. The current U.S. labels do not list NAION. Sudden vision loss needs urgent care either way.

Compounded, counterfeit and research-labeled products

The side effect data above apply to FDA-approved products. The FDA says compounded GLP-1 drugs are not reviewed for safety, effectiveness or quality, and it has received reports of adverse events that may be related to errors in the amount injected with compounded semaglutide, some needing hospitalization. As of May 31, 2026, it had more than 990 adverse event reports for compounded semaglutide and 730 for compounded tirzepatide. Products sold “for research purposes” or in salt forms are not approved drugs, and counterfeits may contain the wrong ingredient or none. Our guides to compounded semaglutide and tirzepatide and approved options explain the rules. Supplements marketed as “GLP-1 support” are not GLP-1 drugs; see what those products contain.

When to contact a clinician promptly

The Medication Guides list symptoms to report right away:

• Severe stomach pain that will not go away, with or without vomiting.
• Pain in the upper stomach, fever, yellowing of the skin or eyes, or clay-colored stools.
• Swelling of the face, lips, tongue or throat, or trouble breathing or swallowing.
• Vomiting or diarrhea that leads to signs of dehydration.
• A lump or swelling in the neck, persistent hoarseness or trouble swallowing.
• Vision changes, especially in people with type 2 diabetes, and any sudden vision loss.
• New or worsening depression or mood changes.

Side effect guides for each GLP-1 drug

• Ozempic and Rybelsus (semaglutide)
• Wegovy injection, pill and Wegovy HD
• Mounjaro (tirzepatide)
• Zepbound
• Saxenda and Victoza (liraglutide)
• Foundayo (orforglipron)
• Retatrutide, an investigational drug

Frequently Asked Questions

Peptide Labs does not sell GLP-1 medicines or any prescription drug. This article is general information, not medical advice. Read the Medication Guide that comes with a prescription, and ask a pharmacist or prescriber how this information applies to you.

Last reviewed September 2026.

Related guides: What Is GLP-1? The Hormone, How GLP-1 Drugs Work and Every FDA-Approved Option, Semaglutide Side Effects: What the Ozempic, Wegovy and Rybelsus Labels Say, Tirzepatide Side Effects: What the Mounjaro and Zepbound Labels Say, GLP-1 Hair Loss: How Common It Is and What Causes It, Ginger for Nausea: What Studies Show, Other Benefits and Side Effects, Ozempic Constipation: Why It Happens and When to Get Help, Ozempic Nausea: How Long It Lasts and What Helps, Sulfur Burps: Causes, Ozempic Burps and When to Worry, Ozempic Diarrhea: How Common It Is and When to Call, GLP-1 Fatigue: Why You Feel Tired and What Helps, Ozempic Muscle Loss: What the Body-Scan Data Show, Ozempic Headache: Label Rates, Causes and Warning Signs, Ozempic Thyroid Cancer Risk: The Boxed Warning Explained, Ozempic Heartburn and Acid Reflux: What the Labels Say, Ozempic Teeth: Dry Mouth, Enamel and What the Evidence Shows.