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

Short answer: The side effects of GLP-1 medicines such as Ozempic, Wegovy, Saxenda and Mounjaro are largely the same: nausea, diarrhoea and constipation, particularly during the dose-escalation phase. Serious side effects such as pancreatitis are rare but require immediate contact with your doctor.

Ozempic, Wegovy, Saxenda and Mounjaro all work via the same or a similar hormonal mechanism and therefore have largely the same side effects. Anyone who still has to choose between these medicines often wonders exactly what GLP-1 side effects entail and whether one medicine is milder than another. This article provides an overview of what you can expect in general, how the medicines differ, and when a side effect is a reason to contact your doctor.

Why do GLP-1 medicines cause similar side effects?

All GLP-1 medicines affect the same hormonal system, which explains why the side effects are so 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 levels rise, inhibits a counteracting hormone that actually raises blood sugar levels, slows down the rate at which the stomach empties and suppresses feelings of hunger in the brain. Together, this leads to more stable blood sugar levels and a reduced appetite.

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

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

The most common side effects of GLP-1 medicines are gastrointestinal symptoms, and these apply equally to semaglutide, liraglutide and tirzepatide. Nausea is the most frequently reported symptom and occurs particularly at the start of treatment or when the dose is increased. In addition, diarrhoea, vomiting, constipation, abdominal pain and reduced appetite occur regularly. A network meta-analysis in the BMJ shows that these gastrointestinal symptoms are a class-wide effect of GLP-1 receptor agonists, regardless of the specific medicine used.

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

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

Serious side effects of GLP-1 medicines are rare, but still require vigilance. Acute pancreatitis, an inflammation of the pancreas, is a rare but serious side effect that can occur with the use of all three medicines. Prolonged vomiting or diarrhoea can also lead to dehydration and, in the worst case, acute kidney failure. Gallstones and an inflamed gallbladder (cholecystitis) are also common risks within this class of medicines.

Furthermore, each medicine has its own specific risk factors. For Wegovy (semaglutide), a very rare eye condition (NAION), in which the optic nerve is damaged, has been reported. This occurs in approximately 1 in 10,000 people per year. A serious allergic reaction may also occur. Furthermore, anyone combining this medicine with insulin or certain diabetes medicines (sulfonylureas) is at greater risk of low blood sugar. When using Saxenda (liraglutide), the skin at the injection site may become hardened or thickened (cutaneous amyloidosis). This occurs particularly if injections are always administered at exactly the same spot. Changing the injection site helps to prevent this. When using Mounjaro (tirzepatide), a slight increase in heart rate has been reported, of around 3 to 5 beats per minute. According to the Farmacotherapeutisch Kompas, these symptoms should always be reported to the treating doctor, even if they are rare.

What are the differences between the GLP-1 medicines?

The medicines are very similar, but differ in a few respects.

Tirzepatide (Mounjaro) is the only medicine 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 appears to be largely the same as that of the other medicines. Liraglutide (Saxenda) must be injected every day, whilst semaglutide (Wegovy) only needs to be administered once a week. This is because liraglutide is broken down more quickly in the body. It is also the only medicine where skin hardening at the injection site may occur. Semaglutide is the only medicine for which hair loss has been observed slightly more frequently (around 2.5 per cent). Would you like to compare the medicines 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 if you are taking GLP-1 medicines?

Contact your doctor immediately if you experience severe, persistent abdominal pain, as this may indicate pancreatitis. Signs of dehydration, such as dizziness, a dry mouth or passing very little urine, are also reasons not to delay. Sudden changes in vision, signs of a severe allergic reaction such as swollen lips or difficulty breathing, and symptoms that seriously impair your daily functioning should all be discussed with your doctor or healthcare provider. This list is not exhaustive: if in doubt, it is always best to get in touch.

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

At Goodweigh, you receive ongoing medical guidance as your dose is gradually increased. This guidance is specifically aimed at minimising side effects and, should they nevertheless occur, at detecting them in good time and adjusting your treatment in consultation with your healthcare provider.

This means you don’t have to decide for yourself whether a symptom is normal or whether it’s a sign that your dose needs adjusting. Would you like to know more about how this support works? Take a look at Goodweigh’s weight loss programme.

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

Most side effects of GLP-1 medicines are a direct result of the same mechanism of action that also enables weight loss. They usually subside as the body gets used to the medication, typically 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 necessary, so that you can safely work towards your goal.