GLP-1 side effects: what can you expect with Ozempic, Wegovy, Saxenda and Mounjaro?

Short answer: The side effects of the GLP-1 medications Ozempic, Wegovy, Saxenda, and Mounjaro are largely the same: nausea, diarrhea, and constipation, especially when the dose is increased gradually. Serious side effects such as pancreatitis are rare but require immediate contact with your doctor.

Ozempic, Wegovy, Saxenda, and Mounjaro all work through the same or a similar hormonal mechanism of action and therefore have largely the same side effects. If you are still deciding between these medications, you may be wondering exactly what GLP-1 side effects entail and whether one medication is milder than the others. This article provides an overview of what you can generally expect, how the medications differ from one another, and when a side effect warrants contacting your doctor.

Why Do GLP-1 Medications Cause Similar Side Effects?

All GLP-1 medications affect the same hormonal system, which explains why the side effects are very similar. Semaglutide and liraglutide mimic a hormone produced naturally by the body: GLP-1. This hormone ensures that the pancreas secretes insulin when blood sugar rises, inhibits a counter-hormone that, on the contrary, raises blood sugar, slows stomach emptying, and suppresses the feeling of hunger in the brain. Together, these effects ensure more stable blood sugar levels and reduced hunger.

Since GLP-1 receptors are also found in the gastrointestinal tract and the brainstem, the known side effects arise precisely through this mechanism. According to research on the efficacy and safety of GLP-1 medications, this is an expected effect of how these drugs work and not a sign that something is going wrong.

What are the most common side effects of GLP-1 medications?

The most common side effects of GLP-1 medications are gastrointestinal symptoms, and these apply equally to semaglutide, liraglutide, and tirzepatide. Nausea is the most frequently reported side effect and occurs especially when starting treatment or increasing the dose. In addition, diarrhea, vomiting, constipation, abdominal pain, and loss of appetite occur regularly. A network meta-analysis in the BMJ shows that these gastrointestinal side effects are a class-wide effect of GLP-1 receptor agonists, regardless of the specific medication used.

For most users, these symptoms subside as the body adjusts to the higher dose. If you’d like to know what this looks like in practice for a specific medication, you can read more about the side effects of Ozempic in detail. Diet also plays a role: what you should eat while taking GLP-1 medication can help alleviate nausea and stomach discomfort.

What serious side effects should you be aware of with GLP-1 medication?

Serious side effects of GLP-1 medications are rare but still require attention. Acute pancreatitis, an inflammation of the pancreas, is a rare but serious side effect that can occur with all three medications. Persistent vomiting or diarrhea can also lead to dehydration and, in the worst case, acute kidney failure. Gallstones and inflammation of the gallbladder (cholecystitis) are also among the risks associated with this class of medications.

In addition, each medication has its own specific focus. For Wegovy (semaglutide), a very rare eye condition (NAION) has been described, in which the optic nerve is damaged. This occurs in approximately 1 in 10,000 people per year. A severe allergic reaction may also occur. And if the medication is combined with insulin or certain diabetes medications (SU derivatives), there is an increased risk of low blood sugar. With Saxenda (liraglutide), the skin at the injection site may become hard or thickened (cutaneous amyloidosis). This occurs especially if you always inject in exactly the same spot. Rotating injection sites helps prevent this. With Mounjaro (tirzepatide), a slight increase in heart rate of approximately 3 to 5 beats per minute has been reported. According to the Farmacotherapeutisch Kompas, these symptoms should always be reported to the treating physician, even if they are rare.

What are the differences between the GLP-1 medications?

The medications are very similar, but differ in a few ways.

Tirzepatide (Mounjaro) is the only one that acts on two hormones simultaneously (GIP and GLP-1). In a study comparing it directly with semaglutide, a slightly different side effect profile emerged, including a slight increase in heart rate. Otherwise, the safety profile is largely similar to that of the other medications. Liraglutide (Saxenda) must be injected daily, while semaglutide (Wegovy) is taken only once a week. This is because liraglutide is eliminated from the body more quickly. It is also the only medication where hardening of the skin at the injection site may occur. Semaglutide is the only medication for which hair loss has been observed slightly more frequently (approximately 2.5%). Would you like to compare these medications in more detail in terms of weight loss, dosage, and efficacy? Then read Ozempic, Wegovy, Mounjaro, and Saxenda Compared.

When should you contact your doctor while using GLP-1 medications?

Contact your doctor immediately if you experience severe, persistent abdominal pain, as this may be a sign of pancreatitis. Signs of dehydration, such as dizziness, dry mouth, or very infrequent urination, are also reasons not to wait. Sudden changes in vision, signs of a severe allergic reaction—such as swollen lips or difficulty breathing—as well as symptoms that significantly impair your daily functioning should all be discussed with your doctor or healthcare provider. This list is not exhaustive: when in doubt, it’s always best to contact your doctor.

How does Goodweigh help manage side effects of GLP-1 medications?

At Goodweigh, you receive ongoing medical guidance as you gradually increase your dose. This guidance is specifically designed to minimize side effects and, if they do occur, to detect them in time and adjust your dosage in collaboration with your healthcare provider.

That way, you don’t have to decide on your own whether a symptom is normal or a sign that your dosage needs to be adjusted. Would you like to learn more about how this guidance works? See the Goodweigh Weight Loss Program.

Side effects of GLP-1 medications are predictable and usually temporary

Most side effects of GLP-1 medications are a direct result of the same mechanism of action that enables weight loss. They usually subside as your body adjusts to the medication, most often within the first few weeks to months after starting treatment or increasing the dose. With medical guidance from Goodweigh, these side effects are monitored and adjusted as needed so you can safely work toward your goal.