Common GLP-1 Side Effects

What you might notice when starting treatment or increasing your dose, what may help, and when to get medical care.

You start a GLP-1 medication and notice that your usual lunch feels too big. A few weeks later, after a dose increase, you’re dealing with nausea or constipation. Is that something you can manage at home, a reason to call your prescriber, or a sign you need urgent care?

Digestive symptoms are among the most common side effects of GLP-1 medications, especially when you start treatment or increase the dose. Mild nausea that passes and still allows you to eat and drink is different from severe abdominal pain or vomiting that prevents you from keeping fluids down. How intense a symptom is, how long it lasts, and what it stops you from doing are often more useful than the symptom name alone. accessdata.fda.gov

This guide focuses on medications such as semaglutide and tirzepatide. Tirzepatide acts on both the GIP and GLP-1 receptors, but it’s commonly included in discussions about GLP-1 treatment. Side effects and instructions can differ by product, dose, and formulation. accessdata.fda.gov

What are the most common GLP-1 side effects?

Nausea, diarrhea, vomiting, constipation, and abdominal discomfort are commonly reported. Some people also experience bloating, burping, indigestion, or reflux. Fatigue and headache are listed for some products, and injectable medications can cause reactions at the injection site. You may experience one symptom, several, or none. accessdata.fda.gov

To put the numbers in context, in adult weight-management trials of Wegovy 2.4 mg injection, about 44% of participants reported nausea, compared with 16% on placebo. Diarrhea was reported by 30% versus 16%, and vomiting by 25% versus 6%. These figures describe reports over the course of specific trials. They don’t tell you how long an individual episode lasted or predict what you’ll experience on a different dose or product. accessdata.fda.gov

One reason digestive symptoms can occur is that these medicines affect appetite and can slow the movement of food out of the stomach. A meal that felt comfortable before treatment may leave you feeling very full. If that starts happening, notice how much you ate, how quickly you ate it, and whether symptoms appeared after a dose change. Those details can help you decide what to try and what to tell your prescriber. accessdata.fda.gov

Nausea and feeling full sooner

Nausea might feel like mild queasiness after lunch or a stronger discomfort that makes it hard to finish a meal. Some people first notice it after a large or rich meal. Others notice it in the days after a dose increase, even when they eat what they normally do. accessdata.fda.gov

If you can still eat and drink, try making the next meal smaller. Put a modest portion on the plate, eat slowly, and pause when you feel comfortably full. You can have more later if you’re hungry. On days when rich or greasy foods make nausea worse, choose a simpler meal you tolerate, such as toast and eggs, soup with crackers, or rice with a small serving of chicken or tofu. Sip fluids regularly. If drinking a large glass with meals makes you uncomfortably full, try sipping between meals. PMC

It’s worth calling your prescriber if you repeatedly can’t finish small meals or nausea is interfering with daily life. Tell them if it began after a dose increase or if you’re eating much less than usual. If your next increase is coming up and symptoms are still bothering you, ask what to do before changing the dose. accessdata.fda.gov

Vomiting and diarrhea

Vomiting and diarrhea can make it hard to replace the fluid you’re losing. Mild symptoms may settle, but pay attention to whether you can keep liquids down and whether you’re urinating about as often as usual. Feeling lightheaded when you stand or passing much less urine than usual can be signs of dehydration. Dehydration can also affect kidney function. accessdata.fda.gov

If you can keep fluids down, take small, frequent sips. Choose foods you tolerate as you feel able to eat. Let your prescriber know if vomiting or diarrhea continues, keeps returning, or is affecting how much you can drink. If you take insulin or another medication that can cause low blood sugar, follow your sick-day plan and ask your diabetes team what to do if you can’t eat normally. accessdata.fda.gov

Get urgent medical care if repeated vomiting prevents you from keeping fluids down, especially if you’re barely urinating, feel faint, or have severe abdominal pain. Vomiting with severe pain deserves evaluation even if it started around the time you increased your dose. accessdata.fda.gov

Constipation

You may go less often than usual, pass harder stools, or need to strain. Sometimes several things change at once. You’re eating smaller meals, drinking less because you feel full, or moving less because you’ve been feeling unwell. Looking at those changes can help you find a reasonable first step. accessdata.fda.gov

If symptoms are mild, drink fluids regularly unless your healthcare team has advised you to limit them. Bring fiber-rich foods back into meals gradually if you’ve been eating less of them. Oats, pears, beans, and cooked vegetables are examples. A short walk can also fit into your routine if you feel well enough. If you’re already bloated or eating very little, a large fiber supplement may be uncomfortable. Ask a pharmacist or clinician before adding one or using a laxative, particularly if constipation persists. PMC

Seek urgent medical care if constipation comes with severe abdominal pain, significant swelling of the abdomen, vomiting, or an inability to pass gas along with those symptoms. That combination needs assessment for causes such as a bowel blockage. accessdata.fda.gov

Bloating, burping, and heartburn

You might notice more pressure after meals, more frequent burping, or a burning feeling that gets worse when you lie down. Start by noticing the circumstances. Did you eat quickly? Was dinner larger or richer than usual? Did you lie down soon afterward? A brief note can help you spot a pattern without having to avoid a long list of foods. accessdata.fda.gov

Try smaller portions and stay upright after eating if lying down makes reflux worse. If a particular food or carbonated drink repeatedly makes you uncomfortable, see how you feel without it for a few meals. If reflux regularly interrupts sleep, or you often need an over-the-counter remedy, speak with your prescriber or pharmacist. And if you develop new chest pressure or discomfort and aren’t sure what’s causing it, seek urgent evaluation. PMC

Headache, fatigue, and injection-site reactions

Headache or fatigue can occur with some products. If you notice either, tell your clinician what else has changed. Have you been able to drink normally? Are you skipping meals because of nausea? If you have diabetes and feel shaky, sweaty, dizzy, or unusually tired, check your glucose according to your care plan. Those symptoms can overlap with low blood sugar. accessdata.fda.gov

Injection-site reactions can include local redness, itching, or discomfort. Follow the instructions for your specific pen or syringe and rotate injection sites as directed. Ask your pharmacist to watch your technique if you’re unsure. Call your healthcare team if a reaction is worsening or spreading. Get emergency help if you develop trouble breathing or swelling of the face, lips, tongue, or throat. accessdata.fda.gov

Can GLP-1 medications cause low blood sugar?

Low blood sugar is a particular concern when a GLP-1 medication is combined with insulin or a sulfonylurea. Before starting or increasing a dose, ask your diabetes team when to check your glucose, what to do if you’re eating less, and whether any other medicine needs adjustment. Follow their instructions for changing doses. accessdata.fda.gov

The CDC considers a blood glucose reading below 70 mg/dL low. For adults who are alert and can swallow safely, the usual 15–15 rule is to take 15 grams of fast-acting carbohydrate, wait 15 minutes, and check again. Repeat if glucose is still below 70 mg/dL. Follow your personal plan for what to eat once it recovers and contact your care team about repeated lows. www.cdc.gov

If someone is unconscious, having a seizure, or unable to swallow safely, call emergency services. Keep food and drink out of their mouth. Give glucagon if available and you know how to use it. If you’re at risk for severe lows, ask your care team whether you should have glucagon and show the people around you how to use it. www.cdc.gov

Less common warning signs worth knowing

These symptoms can have more than one cause. Tell the healthcare team which medication you take, your dose, when you last took it, and when the symptoms started. Wegovy and Zepbound labeling also advises monitoring people with a history of diabetic retinopathy. If you have that history, ask your diabetes or eye-care team about follow-up when starting treatment. accessdata.fda.gov

What does the thyroid warning mean?

Wegovy and Zepbound carry boxed warnings about thyroid C-cell tumors observed in rodents. Whether these drugs cause such tumors in humans is unknown. Their labels say people with a personal or family history of medullary thyroid carcinoma, or with multiple endocrine neoplasia syndrome type 2 (MEN2), should not take them. If you notice a new lump in your neck, persistent hoarseness, or trouble swallowing, contact your clinician. accessdata.fda.gov

What if you have a procedure coming up?

Tell the team planning your procedure if you take a GLP-1 medication and will have anesthesia or deep sedation. Because these drugs can delay stomach emptying, food may remain in the stomach longer. The procedure team may want to know your dose, when you last took it, whether you recently increased it, and whether you have digestive symptoms. Follow their instructions about fasting and managing the medication. accessdata.fda.gov

How long do GLP-1 side effects last?

There’s no single timeline. Digestive symptoms often appear during dose increases and may ease as your body adjusts, but the pattern varies. Nausea after a dose increase may settle while constipation lasts longer. Some people continue to have symptoms at a stable dose. A symptom that keeps coming back, gets worse, or makes it difficult to eat, drink, or work deserves a call even if it seems manageable at first. accessdata.fda.gov

A short record can help your prescriber decide what to do. Write down:

• Your medication and dose, including the date of the last increase.
• When the symptom began and whether it’s getting better or worse.
• What you can eat and drink, especially if you’ve missed meals or vomited.
• Any relevant readings or changes, such as low glucose, reduced urination, or a new medication.

For example, “I increased my dose on Sunday, felt nauseated after meals on Monday and Tuesday, and could still drink normally” gives your clinician something specific to work with. “I’ve been vomiting since last night and can’t keep water down” calls for urgent care. accessdata.fda.gov

Common questions about GLP-1 side effects

Does nausea mean the medication is working?

Treatment benefit is measured by the goal you and your clinician set, such as changes in blood glucose, A1C, or weight over time. You can benefit from treatment without feeling nauseated. If nausea is interfering with meals or fluids, bring it up at follow-up or call sooner if it’s severe. accessdata.fda.gov

Can I take something for nausea, diarrhea, or constipation?

Ask a pharmacist or prescriber before adding a remedy, especially if symptoms persist or you take other medicines. Tell them about abdominal pain, vomiting, or dehydration, which can change what’s appropriate. If you keep needing a remedy just to tolerate your dose, ask your prescriber to review the treatment plan. PMC

Will switching from an injection to a tablet solve digestive side effects?

Tablets can also cause digestive symptoms. A switch may change how you take the medication and how you tolerate it, but the result varies. If symptoms are prompting the switch, tell your prescriber which ones are causing trouble. Ask about the new formulation’s instructions and exactly when you should start it. accessdata.fda.gov

What should I do if I feel unwell before my next dose increase?

Contact your prescriber and explain what you’re experiencing, how long it has lasted, and whether you can eat and drink normally. Ask whether the next increase should go ahead as planned. If you have severe ongoing pain, can’t keep fluids down, or have signs of a serious allergic reaction, seek urgent or emergency care as described above. accessdata.fda.gov

Before your first dose or next increase, write down who to call during office hours, what to do after hours, and which symptoms warrant immediate care. If you’re managing diabetes, keep your low blood sugar and sick-day instructions alongside that information. When you’re feeling unwell, having the plan where you can find it makes the next decision easier.