How GLP-1 medicines work
GLP-1 receptor agonists copy GLP-1, a hormone your gut releases after you eat. They help the pancreas release insulin when blood sugar is high, reduce how much sugar the liver releases, slow how fast the stomach empties, and act on the brain to increase fullness. Eating less is why many people lose weight.
- Semaglutide is sold as Wegovy (weekly injection or daily tablet, for weight and heart risk) and as Ozempic and Rybelsus (for type 2 diabetes).
- Tirzepatide (Zepbound, Mounjaro) acts on the GLP-1 receptor and also on the receptor for GIP, a second gut hormone. See is tirzepatide a GLP-1.
- Older GLP-1 drugs include liraglutide, dulaglutide and exenatide.
Slower stomach emptying explains most of the side effects. Food sits longer, so large, fatty or spicy meals are more likely to cause nausea, reflux and burping.
Common side effects
| Side effect | Wegovy injection vs placebo | Zepbound vs placebo |
|---|---|---|
| Nausea | 44% vs 16% | 25% to 29% vs 8% |
| Diarrhea | 30% vs 16% | 19% to 23% vs 8% |
| Vomiting | 24% vs 6% | 8% to 13% vs 2% |
| Constipation | 24% vs 11% | 11% to 17% vs 5% |
| Abdominal pain | 20% vs 10% | 9% to 10% vs 5% |
Other side effects listed in the labels include heartburn and reflux, burping, bloating and gas, tiredness, dizziness, headache, injection site reactions and hair loss. On Zepbound, hair loss was linked to weight loss and was reported more often in women (7.1%) than men (0.5%).
Most nausea, vomiting and diarrhea happened while the dose was being raised and eased over time. Starting low and stepping up slowly is how clinicians help with tolerance. Smaller meals, stopping when you feel full and staying hydrated also help; see what to eat on a GLP-1.
Serious warnings on the FDA labels
- Thyroid C-cell tumors (boxed warning). These drugs caused thyroid tumors in rats. It isn't known whether they do in humans. They aren't used by people with a personal or family history of medullary thyroid cancer or MEN 2.
- Pancreatitis. Inflammation of the pancreas has been seen with GLP-1 drugs. The labels say to stop the drug if pancreatitis is suspected.
- Gallbladder disease, including gallstones and gallbladder inflammation.
- Kidney injury from dehydration. Vomiting and diarrhea can lead to fluid loss and acute kidney injury.
- Severe stomach and intestinal reactions. The labels don't recommend these drugs for people with severe gastroparesis.
- Low blood sugar when used with insulin or sulfonylureas. Your clinician may lower those doses.
- Diabetic eye disease can worsen in people with type 2 diabetes and a history of diabetic retinopathy.
- Serious allergic reactions, including swelling of the face, lips or throat.
- Aspiration during anesthesia. Food can stay in the stomach, so tell every clinician about your GLP-1 before surgery or sedation.
In 2026, the Wegovy and Zepbound labels removed an earlier warning section on suicidal behavior and thoughts. Still tell your clinician about any new or worsening mood changes.
When to call a clinician
Get medical care right away for stomach pain that is severe or won't go away, with or without vomiting, especially if it spreads to your back; swelling of your face, lips, tongue or throat, trouble breathing or swallowing; yellow skin or eyes, fever or clay-colored stools; very little urine or signs of dehydration; a lump or swelling in your neck, or hoarseness; or vision changes.
Call your clinician soon, not urgently, if nausea or vomiting keeps you from eating or drinking, constipation lasts days, or you feel shaky, sweaty or confused (possible low blood sugar). Don't skip, double or change a dose on your own. Your clinician decides the dose.
Unapproved and compounded products add risk. The FDA has received reports of dosing errors, some needing hospital care, when people measured doses themselves from vials. Compounded medications aren't FDA-approved. A licensed clinician decides what's right for you.
Getting a GLP-1 through Gabriel
If you send a prescription request, a licensed clinician reviews your health history and decides whether a GLP-1 is appropriate. You can also ask Gabriel free about side effects any time by app, web or text.
Common questions
What are the most common side effects of GLP-1 medications?
Nausea, diarrhea, vomiting, constipation and stomach pain. They are most common while the dose is being raised and often ease over time.
How long do GLP-1 side effects last?
In the Zepbound trials, most nausea, vomiting and diarrhea happened during dose increases and decreased over time. If symptoms are severe or don't improve, call your clinician.
Do GLP-1 drugs cause thyroid cancer?
They caused thyroid C-cell tumors in rats, and it isn't known whether they do in humans. That is why the labels carry a boxed warning and why people with a personal or family history of medullary thyroid cancer or MEN 2 don't use them.
Can GLP-1s cause hair loss?
Hair loss is listed on the Wegovy and Zepbound labels. On Zepbound it was linked to weight loss and was more common in women than men.
Should I stop my GLP-1 before surgery?
Tell your surgeon and anesthesia team you take it. The labels warn about food being inhaled into the lungs during anesthesia or deep sedation, and your care team will tell you what to do.
Sources
- Wegovy (semaglutide) prescribing information, revised 06/2026 Novo Nordisk
- Zepbound (tirzepatide) prescribing information, revised 08/2026 Eli Lilly
- GLP-1 Agonists: What They Are, How They Work and Side Effects Cleveland Clinic
- Semaglutide Injection MedlinePlus
- FDA's concerns with unapproved GLP-1 drugs used for weight loss U.S. Food and Drug Administration
This guide is general information, not medical advice. It does not replace a visit with a licensed clinician. Gabriel membership is not health insurance.