GLP-1 medicines and your digestive system

Semaglutide (Ozempic, Wegovy, Rybelsus), tirzepatide (Mounjaro, Zepbound), liraglutide and similar medicines have changed how many people manage diabetes and weight. Patients across Los Angeles are taking them, often for the first time. Because these medicines act on the stomach and gut, it helps to know what is normal, what you can do about side effects, and when to call your doctor.

How do GLP-1 medicines affect digestion?

GLP-1 (glucagon-like peptide-1) is a hormone your gut makes after you eat. It tells your pancreas to release insulin, signals your brain that you are full, and slows how quickly food leaves your stomach. GLP-1 medicines copy this hormone, and some, like tirzepatide, also act on a second hormone called GIP.

Slower stomach emptying is part of how these medicines help you feel full on smaller meals. It is also why many of their side effects show up in the digestive system. Food stays in the stomach longer, the intestines move more slowly, and eating too much or too fast can quickly make you feel unwell.

Side effects are most common when you first start and each time the dose goes up. For many people, they ease over several weeks as the body adjusts. This is one reason doctors raise the dose slowly, step by step.

Common side effects and what helps

Not everyone has side effects, and most are mild to moderate. Here are the most common ones and practical ways to manage them.

Nausea

Nausea is the most common side effect, especially in the first weeks and after a dose increase.

• Eat smaller meals and stop as soon as you feel full, even if food is left on the plate.
• Eat slowly. It can take 20 minutes or more to notice fullness.
• Choose lighter foods. Fried, greasy and very rich foods are common triggers.
• Sip fluids through the day instead of drinking large amounts at once.

Constipation

Slower movement through the intestines, along with eating and drinking less, can lead to constipation.

• Drink water steadily through the day. Many people drink less without noticing because they feel full.
• Add fiber gradually from vegetables, fruit, beans and whole grains, or a fiber supplement.
• Stay active. A daily walk helps the bowels move.
• Ask your doctor before using laxatives regularly. Our constipation page has more ideas.

Reflux, burping and heartburn

When food stays in the stomach longer, some people notice acid reflux, burping or a sour taste, especially at night.

• Avoid lying down for two to three hours after eating.
• Make dinner your smallest meal, and eat it earlier in the evening.
• Cut back on carbonated drinks, alcohol and large fatty meals.
• If heartburn is frequent, read our acid reflux and GERD page and talk with your doctor.

Diarrhea, bloating and vomiting

Some people have loose stools, gas or bloating, or occasional vomiting, usually early on. Eating smaller portions and avoiding very fatty foods often helps. Drink enough fluids to replace what you lose.

When do side effects need a call?

Most digestive side effects are uncomfortable but not dangerous. A few symptoms need prompt attention, because GLP-1 medicines have been linked, uncommonly, to more serious problems such as pancreatitis (inflammation of the pancreas), gallbladder problems and severe dehydration. Call your doctor the same day if you have:

• Vomiting or diarrhea that keeps you from keeping fluids down for a day
• Signs of dehydration: very little urine, dark urine, dizziness or a racing heart
• Pain in the upper right belly, fever, or yellowing of the skin or eyes
• No bowel movement for several days along with bloating, belly pain or vomiting
• New trouble swallowing, or food that feels stuck

Before an endoscopy or colonoscopy: tell your GI doctor

Because GLP-1 medicines slow stomach emptying, food can still be in the stomach many hours after a meal, even when you have followed the usual fasting rules. During sedation, food or liquid left in the stomach can come back up and enter the lungs. This is called aspiration, and it is the main safety concern. Slower bowels may also make it harder to get a clean colon for a colonoscopy.

Guidance on this has changed as experts have learned more. In 2024, several national medical societies, including the American Gastroenterological Association, published joint guidance. In general terms, it says:

• The decision is individualized. Many patients can continue their GLP-1 medicine before a procedure.
• People who are at higher risk, such as those just starting, increasing their dose, or having nausea, vomiting or bloating, may be asked to hold a dose.
• A clear liquid diet for the day before the procedure may be advised, even for an upper endoscopy.
• If you have significant nausea, vomiting or bloating on the day of the procedure, it may need to be rescheduled for your safety.

What this means for you: tell the office about any GLP-1 medicine when you schedule, including the name, dose, how often you take it and the day of your last dose. Include medicines bought through online programs or compounding pharmacies. Then follow the instructions you are given. Do not stop or skip a dose on your own, especially if you take it for diabetes, because your blood sugar may need a plan too.

Our day-by-day colonoscopy prep guide walks through the rest of the preparation. Dr. Pimienta performs colonoscopy and upper endoscopy at Specialty Surgical Center of Beverly Hills, and your instructions will be written for your medicines.

Weight management with a doctor

GLP-1 medicines can be very helpful, but they work best as part of a broader plan. Losing weight quickly can cost muscle as well as fat, so eating enough protein and doing some strength exercise matter. Stopping the medicine often leads to some weight coming back, which is worth discussing before you start. Your doctor will also review your other medicines, check for conditions where these drugs are not recommended, and monitor side effects over time.

Dr. Pimienta is triple board-certified in gastroenterology, obesity medicine and internal medicine. That combination is useful when weight, reflux, constipation, fatty liver and other digestive concerns overlap. Through medical weight management, he looks at eating patterns, activity, sleep, other medicines and your goals, and helps you decide whether medicine fits. Your plan depends on your health; Dr. Pimienta will talk with you about what fits you. If you have fatty liver, our article on what your liver tests mean may help too.

A note on safety: the FDA has warned about dosing errors and unapproved versions of these medicines sold online. Get them through a licensed prescriber and pharmacy, and make sure you understand your dose and how to measure it.

When to see a GI doctor

Consider seeing a gastroenterologist if digestive side effects last beyond the first few weeks, if heartburn, constipation or bloating keeps you from staying on a medicine that otherwise helps you, if you have a procedure coming up and are not sure what to do with your dose, or if you want a medical plan for weight loss. Dr. Pimienta sees adults from across Los Angeles County, in English and Spanish, at the Wilshire office or by secure video for patients in California. To get started, request an appointment and the team will call you back.

References

1. Multisociety Clinical Practice Guidance for the Safe Use of Glucagon-like Peptide-1 Receptor Agonists in the Perioperative Period. Clinical Gastroenterology and Hepatology. 2024.
2. National Institute of Diabetes and Digestive and Kidney Diseases. Prescription Medications to Treat Overweight and Obesity.
3. MedlinePlus (National Library of Medicine). Semaglutide Injection.
4. U.S. Food and Drug Administration. Medications Containing Semaglutide Marketed for Type 2 Diabetes or Weight Loss.