GLP-1 Medications and Side Effects: What Patients Should Know

by Anthony J. Millard, MD

Winter 2026

 

What are GLP-1s and how do they work?

GLP-1 medicines have become more common in recent years, but they have been used for about 20 years. GLP-1 is a hormone the body makes naturally, but it only works for a short time. GLP-1 medicines are designed to act like this hormone while lasting longer in the body.

For people with diabetes, GLP-1 helps the body recognize when blood sugar is too high. It supports the release of insulin to lower blood sugar without causing it to drop too low. Researchers have also learned that GLP-1 affects parts of the brain that control hunger. Weekly injectable GLP-1 medicines such as semaglutide or tirzepatide, which also works on a hormone called GIP, can help people feel full sooner, think about food less often and have fewer cravings. These effects can support long-term weight loss.

Why side effects can happen

No medicine offers only benefits. GLP-1 medicines can cause side effects and this is one reason some people stop taking them. Data published in the journal Obesity shows that slightly more than 50% of patients stop using semaglutide or tirzepatide for obesity treatment within a year. A common reason for stopping is side effects, which are often related to the stomach and digestion. These can include nausea, vomiting, constipation and/or diarrhea.

Side effects happen because GLP-1 affects more than one area of the body. Nausea is linked to how GLP-1 works in a part of the brain that is separate from appetite control. When nausea is strong, it can lead to vomiting. Experts are still learning why GLP-1s can cause diarrhea, but possible reasons include changes in how food moves through the gut or how the stomach and intestines communicate with each other.

Constipation may also happen, often because people eat less while taking these medicines. Eating less means there is less waste for the body to move through the intestines. Fewer bowel movements are usually not a problem unless they cause symptoms such as abdominal pain, bloating, cramping or nausea.

How food choices can affect side effects

Nausea while taking a GLP-1 can be linked to what you eat or how much you eat. High-fat foods are often the first foods to limit. These can include foods that are fried or high in oil, cheese or butter, such as burgers, pizza or fries. They can also include ice cream or other dairy products with higher fat content, such as 2%–4% fat, as well as healthier fats found in foods like salmon, avocado or nuts.

This does not mean these foods must be avoided completely, especially healthier fats. However, if nausea is a problem, it can help to look closely at whether any of these foods are making symptoms worse.

Portion size and eating pace matter

Portion size plays an important role in how your body responds to a GLP-1. A common starting point is to cut portions in half compared with what you are used to eating. If nausea continues and does not seem related to the type of food, eating an even smaller portion may help.

Eating slowly can also make a difference. Taking about 15–20 minutes to eat a meal gives your body time to notice when you are full. You can always eat a little more if you are still hungry. Eating too much or too quickly can lead to nausea or other discomfort. Finding the right portion size and eating pace can help limit side effects and make it easier to stay on the medicine long enough to see its full benefits

Balancing benefits and side effects

For some people, side effects may be a reason not to use a medicine. For others, the benefits may be strong enough to weigh against the side effects, especially when those side effects can be managed with guidance from a health care provider. This is how GLP-1 obesity medications should be considered.

These medicines can help people manage excess weight in ways that may have felt out of reach before. Weight loss and long-term weight management may also help improve other health conditions. The benefits of medicines like semaglutide and tirzepatide can be significant. However, the first goal is making sure each person can tolerate the medicine. Without that, the benefits are often harder to achieve.

Using dose adjustments to reduce side effects

Another way to limit side effects is to increase the dose slowly over time. This gives the body more time to adjust to the medicine. If a lower dose works well and does not cause side effects, there may be no need to increase it.

Semaglutide and tirzepatide are taken once a week. People usually stay on the same dose for at least four weeks so the body can adjust. Some people do well on a certain dose and may stay there longer. Health care providers focus on finding the lowest dose that works with few or no side effects and keeping that dose as long as it continues to help.

What progress can look like

There is no single pace of weight loss that is right for everyone. Progress can look different from person to person. A helpful way to judge whether a GLP-1 medicine is working is to notice changes such as thinking about food less often, feeling full sooner and having fewer cravings. Weight loss may range from about two pounds per month to two pounds per week depending on your life situation, medical history and personal goals.

A more personalized approach

Another way to reduce side effects is called flexible titration. This means increasing the dose more slowly than usual. Using semaglutide as an example, standard dosing starts at 0.25 mg per week and increases every four weeks. In one study from Israel, researchers compared this standard schedule with a slower increase that took 16 weeks to reach a 1 mg dose.

People who followed the slower increase had fewer side effects. At the same time, improvements in blood sugar levels and weight loss were similar in both groups. This approach is considered off-label and is only possible with certain delivery systems. However, it shows how a more personalized dosing plan may help more people tolerate obesity medications over the long term.

Managing side effects when they persist

Medicines to help with nausea, such as ondansetron, or treatments for constipation or diarrhea may be used when needed. However, many patients and health care providers prefer to avoid adding more medicines when possible.

If side effects continue, switching to a different 

weekly injectable option may help. Some people tolerate one medicine better than another. Older but still effective obesity medications may also be an option. 

For some individuals, metabolic or bariatric surgery, such as gastric sleeve, gastric bypass or endoscopic sleeve procedures, may be appropriate. Using medication before or after surgery or endoscopy is another possible approach. A board-certified obesity medicine specialist can help create a plan based on a person’s medical history and goals. You can find a provider who specializes in obesity care at ObesityCareProviders.com.

Looking ahead: What’s next in obesity treatment?

It is possible that the right treatment is not available yet. The future looks promising as research continues and new options become available. For people who have not found the right fit, new obesity medications offer real hope.

In December 2025, the U.S. Food and Drug Administration approved the first GLP-1 pill for obesity. It is taken once a day and is expected to be available in 2026. Studies showed that people taking the pill lost a significant amount of weight, similar to results seen with weekly injections.

Other daily GLP-1 pills are still being reviewed and may become available in the future. New weekly and monthly injectable medicines are also being studied. These options may give people more choices and make treatment easier to fit into daily life in ways that feel more manageable and realistic.

June 2026 will mark five years since GLP-1 medications were approved for obesity and overweight. This early period will likely be remembered with both excitement and frustration. Many people have seen meaningful progress and improvements in their health, while others have faced real challenges. Some have struggled with high costs or limited insurance coverage, which can put treatment out of reach.

The Obesity Action Coalition is working to address these barriers and support people living with obesity. Looking ahead, new treatment options and growing experience among healthcare providers may help improve access and affordability. With many new options in development, the chances of finding a treatment that works well for you continue to grow.

When to call your provider

• You have severe side effects that interfere with your ability to get through your day.
• You have not noticed any benefit after 3–4 weeks at a dose and do not have instructions on when to increase it.

 

About the Author: 

Anthony J. Millard, MD, is board-certified in internal medicine and obesity medicine. Previously on staff at the University of Colorado and Northwestern Medicine in Chicago, he is exploring his next role in patient care. In the meantime, he shares evidence-based content on weight management on Instagram at @drtonymillard.