Side effects and safety: questions and answers

The most common side effects are stomach-related: nausea, diarrhea, vomiting, constipation, stomach pain, heartburn, burping and bloating. Fatigue, headache and dizziness also show up in some labels.

Per the Wegovy label, 44% of people on 2.4 mg reported nausea vs 16% on placebo. Per the Zepbound label, nausea ranged from 25% to 29% vs 9% on placebo. Most cases were mild to moderate. Our side effects hub breaks each one down.

For many people, stomach side effects are worst in the first weeks of treatment and after each dose increase, then ease over the following weeks. In the trials, they were mostly mild to moderate and most frequent during dose escalation.

Constipation can last longer for some people. If a side effect is not easing after a few weeks at the same dose, tell your prescriber, who may hold you at a dose longer. Try the side effect timeline tool.

Stomach side effects such as nausea often appear within a day or two after a weekly injection and may fade toward the end of the week. Patterns vary from person to person.

Eating large or fatty meals in the first days after a shot tends to make symptoms worse. Some people keep a simple log of dose day, meals and symptoms, which makes it easier to spot triggers and to describe the pattern to a prescriber.

Each dose step raises the drug level in your body, and your gut needs time to adjust again. That is why labels start low and step up slowly, usually every 4 weeks for weekly injections.

A flare after a step usually settles within a few weeks. If it does not, your prescriber may keep you at the current dose longer. The Wegovy label, for example, allows delaying the next increase by 4 weeks if a step is not tolerated.

Yes, nausea is the most common side effect of Ozempic and other GLP-1 medicines. Per the Ozempic label, 16% to 20% of people on 0.5 mg or 1 mg reported nausea vs 6% on placebo.

It is usually worst early on and after dose increases. Smaller meals, eating slowly, avoiding greasy food and sipping fluids often help. Tell your prescriber if you cannot keep fluids down. See our nausea guide for more tips.

Yes, some people have both at different times. GLP-1 medicines change how the gut moves food and fluid, and eating much less changes stool volume too.

Per the Zepbound label, diarrhea affected 19% to 23% and constipation 11% to 17% of people, vs 7% and 6% on placebo. Fluids, slowly added fiber and regular walks help many people. Ongoing diarrhea, blood in stool or signs of dehydration need a call to your prescriber. More on constipation.

Sulfur burps, which smell like rotten eggs, are likely linked to food sitting longer in a slowly emptying stomach. Burping is listed on the Zepbound label in 3% to 6% of people vs under 1% on placebo.

Many people find smaller meals, eating slowly, and cutting back on fatty foods, fizzy drinks and some sulfur-rich foods like eggs or cruciferous vegetables helps. If burps come with severe pain or vomiting, contact your prescriber. See burping on a GLP-1.

Fatigue is a listed side effect. Per the Zepbound label, 5% to 7% of people reported fatigue vs 3% on placebo. Eating much less, low protein, dehydration and poor sleep can all add to it.

Many people feel better when they eat regular small meals with protein, drink enough fluids and stay active. Ongoing exhaustion, dizziness on standing or shortness of breath should be checked by a clinician. Read more about fatigue on a GLP-1.

Yes. Per the Wegovy label, headache was reported by 14% of people on 2.4 mg vs 10% on placebo, and dizziness by 8% vs 4%.

Dehydration and eating too little are common contributors, so fluids and regular meals often help. If you also take blood pressure or diabetes medicine, dizziness may mean those doses need review, so tell your prescriber. Sudden severe headache, fainting or confusion needs urgent care. See our page on dizziness.

The main sign is severe stomach pain that will not go away, with or without vomiting, sometimes spreading to your back. All GLP-1 labels warn about acute pancreatitis.

If this happens, stop the medicine and get medical care right away. If the pain is severe and comes with fainting, fast heartbeat or confusion, call 911. Tell your prescriber before starting if you have ever had pancreatitis. More safety details are on the Zepbound warnings page.

Yes. Gallstones and gallbladder inflammation were more common in GLP-1 trials than with placebo, especially with rapid weight loss. Fast weight loss from any cause raises gallstone risk.

Watch for pain in the upper right belly, fever, yellowing of the skin or eyes, or clay-colored stools, and contact your prescriber promptly if they appear. Severe pain with a high fever needs same-day care. The labels list gallbladder disease among their warnings.

It is not known whether GLP-1 medicines cause thyroid cancer in people. They carry a boxed warning because they caused thyroid C-cell tumors in rodent studies.

Because of that, the labels say not to use them if you or a family member has had medullary thyroid carcinoma (MTC), or if you have MEN 2. Tell your prescriber about a lump or swelling in your neck, hoarseness, trouble swallowing or shortness of breath. See the Wegovy warnings.

Routine thyroid tests are usually not required. The Wegovy and Zepbound labels say routine monitoring of calcitonin, a blood marker, or thyroid ultrasound is of uncertain value for catching medullary thyroid cancer early in people taking these medicines.

What matters more is your family history and reporting symptoms such as a neck lump, hoarseness or trouble swallowing. Your prescriber may order tests if you have symptoms or other reasons for concern.

Ozempic and other GLP-1 medicines are not known to damage healthy kidneys directly, but vomiting and diarrhea can cause dehydration, which can worsen kidney function. The labels warn about this, especially in people who already have kidney disease.

Drink fluids and call your prescriber if you cannot keep them down. Ozempic is also approved to reduce the risk of kidney disease worsening in certain adults with type 2 diabetes. See our guide to dehydration on a GLP-1.

On its own, a GLP-1 medicine rarely causes low blood sugar. The risk rises when it is combined with insulin or a sulfonylurea, so your prescriber may lower those doses.

Signs include shakiness, sweating, fast heartbeat, confusion and dizziness. Treat mild lows as your care plan advises. If someone is confused, unable to swallow safely, having a seizure or passing out, call 911. Learn more about low blood sugar.

Tell your surgical and anesthesia team you take a GLP-1 well before any procedure that uses anesthesia or deep sedation. The labels warn that food can stay in the stomach longer, which raises the risk of breathing stomach contents into the lungs (aspiration).

Your team will tell you whether to hold a dose or follow a liquid diet beforehand. Do not stop on your own without asking. Our guide to GLP-1 before surgery covers the details.

No, weight-management GLP-1 medicines are not recommended during pregnancy. The Wegovy and Ozempic labels advise stopping at least 2 months before a planned pregnancy because semaglutide stays in the body for weeks. The Zepbound label says it is not recommended during pregnancy.

If you become pregnant while taking one, contact your prescriber promptly. Weight loss can also improve fertility, so plan birth control with your prescriber. See GLP-1, pregnancy and birth control.

Yes, tirzepatide can make birth control pills less effective because it slows stomach emptying, which can reduce how much of the pill is absorbed. This applies to both Zepbound and Mounjaro.

The labels advise switching to a non-oral method, or adding a barrier method such as condoms, for 4 weeks after starting and for 4 weeks after each dose increase. Implants, IUDs, injections and rings are not affected in the same way. Ask your prescriber which option fits you.

There is limited information on GLP-1 medicines during breastfeeding, so the decision is made case by case with your prescriber and your baby's pediatrician.

The labels for oral semaglutide tablets advise against breastfeeding because an ingredient that helps absorption may build up in a nursing infant. For injectables, labels say to weigh the benefits of breastfeeding against the mother's need for the medicine. Many clinicians suggest waiting until breastfeeding ends before starting a weight-management GLP-1.

Hair loss is reported with GLP-1 medicines, usually as temporary shedding linked to rapid weight loss. Per the Wegovy label, 3% of people on 2.4 mg reported hair loss vs 1% on placebo. Per the Zepbound label, it was 4% to 5% vs 1%.

This type of shedding often improves within months as weight stabilizes. Eating enough protein and calories may help. See a clinician if it is patchy or severe. Read our page on hair loss.

Ozempic face is a popular term, not a medical diagnosis, for a thinner or older-looking face after significant weight loss. It happens because fat is lost from the face along with the rest of the body, and skin may not tighten right away.

It is not listed as a drug side effect on the labels and can happen with any large weight loss. Slower loss, enough protein and good skin care may help. More on loose skin after weight loss.

In January 2026, the FDA said its review of 91 placebo-controlled trials found no increased risk of suicidal thoughts or behavior with GLP-1 medicines, and asked makers of Wegovy, Zepbound and Saxenda to remove that warning. Some labels may still show the older wording.

Tell your prescriber about any mood changes. If you have thoughts of harming yourself, call or text 988. If you are in immediate danger, call 911.

GLP-1 medicines slow stomach emptying on purpose, and the labels say they are not recommended for people who already have severe gastroparesis. Reports of intestinal blockage (ileus) have also been added to labels from postmarketing reports.

Contact your prescriber about vomiting undigested food hours after eating, severe bloating or no bowel movements with belly pain. If you have severe belly pain with repeated vomiting and cannot pass gas, call 911 or go to an emergency room.

Serious allergic reactions are rare but can happen. Signs include swelling of the face, lips, tongue or throat, trouble breathing or swallowing, a severe rash or itching, fainting and a very fast heartbeat.

If you have trouble breathing or throat swelling, call 911. Mild redness or itching at the injection site is different and more common. A known serious allergy to the medicine is a reason not to use it, per the labels.

Mild redness, itching or a small bump where you injected is common and usually fades within a few days. Per the Zepbound label, injection-site reactions were reported by 6% to 8% of people vs 2% on placebo.

Rotating sites each week helps. Contact your prescriber if the area becomes hot, very painful, spreads or oozes, which can signal infection. See injection-site reactions.

In people with type 2 diabetes, rapid improvement in blood sugar has been linked to temporary worsening of diabetic retinopathy. Per the Ozempic label, retinopathy complications were seen more often in a cardiovascular outcomes trial.

If you have diabetic eye disease, your prescriber may want regular eye exams. Report any change in vision, such as blurring, new floaters or sudden vision loss, promptly. Sudden loss of vision in one eye needs emergency care.

Yes, GLP-1 medicines can raise resting heart rate by a few beats per minute, which the labels list as a known effect. For most people this is small and not noticeable.

Tell your prescriber if you feel a racing or pounding heart at rest that lasts. Chest pain, fainting or a racing heart with shortness of breath needs urgent attention, and if symptoms are severe, call 911.

Signs of dehydration include dark urine, peeing much less than usual, dizziness when standing, dry mouth, headache and a racing heart. On a GLP-1 it often follows vomiting or diarrhea, or simply drinking less because you feel full.

Sip fluids through the day and call your prescriber if you cannot keep fluids down for a day. If someone faints, is confused or cannot stay awake, call 911. Our water intake calculator gives a daily target.

Go to an emergency room or call 911 for trouble breathing, swelling of the face or throat, severe belly pain that will not stop, especially with vomiting or pain spreading to your back, fainting, confusion or seizure, or chest pain.

Same-day care is also needed for upper right belly pain with fever or yellow eyes, vomiting with no fluids kept down for a day, or very little urine. For anything life-threatening, call 911 rather than waiting for your prescriber.

GLP-1 medicines have been used for type 2 diabetes since 2005, when exenatide was approved, and liraglutide since 2010, so there is long experience with the class. Heart outcome trials followed people for several years.

Weight-management doses are newer, and very long-term data is still building. The labels list the known risks, and your prescriber weighs them against the health risks of obesity. Regular check-ins help catch problems early. More context: are weight-loss injections safe.