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Can weight loss injections cause stomach problems?
Yes, some people may get stomach problems when using weight loss injections (WLIs). But for more troublesome side effects that require someone to stop treatment, the risk is small.
Your doctor will assess your risk of stomach problems during consultation to make sure the treatment is safe and suitable for you.
Medically reviewed by
Alexandra Cristina Cowell, Writer & Clinical Content Reviewer
- Weight loss injections like semaglutide and tirzepatide often cause nausea, vomiting, constipation, and diarrhoea, especially early in treatment.
- Conditions like gastroparesis, pancreatitis, and bowel obstruction affect fewer than 1% of users.
- GLP-1s can rebalance gut bacteria, reduce inflammation, and improve metabolic and cardiovascular health despite possible GI discomfort.
- For most users, the benefits of GLP-1 injections, such as weight loss and reduced heart disease risk, outweigh the small chance of serious side effects or complications.
Which stomach problems are GLP-1s associated with?
The following are the possible stomach problems someone might experience when using glucagon-like peptide-1 (GLP-1) treatments:
Gastrointestinal (GI) side effects
Gastrointestinal (GI) refers to the gastrointestinal tract, a series of tubes that starts at the mouth and ends at the anus, and includes organs such as the oesophagus, stomach, and upper and lower intestine.
Nausea, vomiting, constipation, and diarrhoea are the most common side effects of WLIs. This is because WLIs increase the levels of GLP-1 in your body, the hormone responsible for appetite regulation and satiety. At higher concentrations, this hormone can induce feelings of nausea and vomiting.
How elevated is the risk of GI side effects?
Almost all GLP-1 weight loss injections have been reported to cause nausea, vomiting, diarrhoea, and constipation, especially in the first few weeks of use. As the body adjusts to the medication, these side effects should subside. But someone might experience side effects again after each dosage increase.
The prevalence of GI side effects also depends on the type of WLIs you’re using. Some research suggests that people are less likely to experience GI side effects with tirzepatide (the active ingredient in Mounjaro) than with semaglutide (the active ingredient in Wegovy). The side effects also tend to be mild; only 5.6% of patients discontinued treatment with semaglutide due to GI side effects, compared to 2.7% in the tirzepatide group.
What can be done to help reduce the risk?
A couple of things you can do to reduce the risk of GI side effects include:
- Eating bland foods with a less prominent flavour to help reduce nausea.
- Eating smaller, more frequent meals. This makes it easier for your body to digest and reduces the risk of diarrhoea and constipation.
- Remaining on your current dose until the side effects become manageable.
Gastroparesis
Gastroparesis is a condition where the stomach empties more slowly than usual. This can lead to symptoms like nausea, feeling full quickly, bloating, abdominal pain, and heartburn.
One potential cause of gastroparesis is the action of GLP-1, which works by delaying stomach emptying to keep you feeling fuller for longer. While this helps reduce your appetite, it may also cause unpleasant side effects.
How elevated is the risk of gastroparesis?
The risk of developing gastroparesis while taking GLP-1 injections is thought to be less than 1%. It’s also worth noting that the risk is greater for people using semaglutide than for those using liraglutide.
Additionally, many individuals may experience symptoms similar to gastroparesis without actually having the condition. If you develop symptoms, it’s best to check with a doctor so they can provide a correct diagnosis.
What can be done to help reduce the risk?
Here are some things you can do to prevent gastroparesis:
- Avoid high-fat, oily foods. These foods are harder to break down, which can worsen symptoms.
- Eat smaller, more frequent meals to make it easier for your stomach to digest food. This also helps maintain your blood sugar levels, which reduces feelings of nausea.
- Don’t eat close to bedtime, as this will increase your risk of heartburn.
- Avoid eating foods that contain insoluble fibre, like wholegrain bread, beans, nuts and seeds, and some vegetables and fruits.
Pancreatitis
Pancreatitis is when the pancreas, an organ that helps with digestion, becomes inflamed. The main symptom includes severe upper abdominal pain, with other symptoms being nausea, vomiting, shortness of breath, and a fast heartbeat.
There are several reasons why you might get pancreatitis while on GLP-1 injections. One reason is that GLP-1 activates pancreatic cells, causing them to grow, which can eventually lead to pancreatitis. Another reason is that rapid weight loss can result in pancreatitis, as it increases the risk of gallstone formation.
How elevated is the risk of pancreatitis?
GLP-1 injections like semaglutide and tirzepatide have been linked to pancreatitis, but the risk of actually getting it is thought to be small. One study found that the incidence of pancreatitis was below 1% per year for semaglutide and liraglutide.
What can be done to help reduce the risk?
There are some things you can do to reduce the risk of pancreatitis, such as:
- Reducing alcohol intake to avoid damaging the pancreas.
- Eating a healthy, well-balanced diet to prevent gallstones.
- Managing your blood sugar levels, as unregulated levels can increase the risk of pancreatitis.
Bowel obstruction
A bowel obstruction is a partial or complete blockage of the intestines, resulting in symptoms like constipation, bloating, flatulence, and abdominal pain. As GLP-1 injections delay stomach emptying, it can lead to the buildup of food in the bowel.
How elevated is the risk of a bowel obstruction?
Studies have shown that the risk of bowel obstruction is four times higher in people using certain GLP-1 injections than in those without the medicine. This risk can be even greater for people with a history of gastrointestinal issues. So your doctor will review your medical history before prescribing any GLP-1 medication to ensure it’s safe for you.
But not all WLIs increase the risk of bowel obstruction substantially. In one study, patients using semaglutide had no increased risk compared to liraglutide, which has a risk of less than 1%.
What can be done to help reduce the risk?
Some things you can do to lower the risk of bowel obstruction include:
- Eating smaller, more frequent meals, so it’s easier for your body to digest.
- Avoiding high-fibre foods. While fibre is important, too much of it can increase the risk of bowel blockage.
- Exercising regularly, as this helps keep your bowels moving.
- Drinking plenty of water to help break down food and soften your stools.
What’s the risk of these side effects in real terms?
GI issues are the side effects with the highest likelihood when using GLP-1 medications. For instance, among patients taking semaglutide, around 43% reported nausea, 30% experienced diarrhoea, and 25% reported vomiting. Similarly, those using tirzepatide reported comparable rates of GI side effects, with nausea occurring in 12%-24%% of patients, diarrhoea in 12%-22%, and vomiting in 2%-13%, depending on the study. But in almost all cases, these side effects were mild to moderate, meaning they were manageable or subsided with time.
The risk of other stomach problems like gastroparesis, pancreatitis, and bowel obstructions is relatively small, with the risk of each thought to be lower than 1%.
Can weight loss injections improve stomach health?
GLP-1s can improve stomach health in several ways. One example is thought to be by rebalancing the gut microbiome. This is a collection of bacteria and other microorganisms that are vital for a healthy body.
Obesity can disrupt the microbiome, which can lead to fat storage, chronic inflammation, and bloating. GLP-1s have been shown to promote beneficial bacteria and reduce negative bacteria. This can help reduce inflammation and improve overall metabolic health.
In addition to improving stomach health, other GLP-1 benefits include enhanced cardiovascular health, better joint function, increased movement and stability, and improved brain health.
Do the benefits outweigh the risks?
Overall, research has shown that the benefits of GLP-1 medications significantly outweigh the risks. GLP-1 medications can help prevent serious conditions such as heart disease and stroke, while also improving overall health. The benefits of these medications generally outweigh the risk of serious stomach issues, which are thought to occur in fewer than 1% of cases.
A prescribing clinician will take your health seriously and monitor you throughout your treatment. They should be transparent about the risks associated with your treatment and will help you understand the symptoms to watch out for.
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