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

Short answer: The side effects of GLP-1 medicines – Ozempic, Wegovy, Saxenda and Mounjaro – are largely the same: nausea, diarrhoea and constipation, particularly when the dose is increased. Serious side effects, such as pancreatitis, are rare, but if they occur, you must contact your doctor immediately.

Ozempic, Wegovy, Saxenda and Mounjaro all work via the same or a similar hormonal mechanism, which is why they largely share the same side effects. Those who have yet to choose between these medicines often wonder exactly what GLP-1 side effects entail and whether one medicine is gentler than another. This article provides an overview of what to expect at the level of this class of medicines, how the medicines differ from one another, and when a side effect is a reason to contact a doctor.

Why do GLP-1 medicines have similar side effects?

All GLP-1 medicines act on the same hormonal system, which explains why their side effects are very similar. Semaglutide and liraglutide mimic the body’s own hormone: GLP-1. This hormone triggers the pancreas to release insulin when blood sugar levels rise, blocks the action of the counter-regulatory hormone that causes blood sugar to rise, slows down the emptying of the stomach and suppresses the feeling of hunger in the brain. Together, these factors ensure more stable blood sugar levels and reduce appetite.

As GLP-1 receptors are also found in the gastrointestinal tract and the brainstem, the known side effects result from the same mechanism. According to studies on the efficacy and safety of GLP-1 medicines, this is an expected effect arising from their mechanism of action, rather than 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 side effect, and it occurs particularly when treatment is started or the dose is increased. In addition, diarrhoea, vomiting, constipation, abdominal pain and loss of appetite occur regularly. According to a network meta-analysis published in the BMJ, these gastrointestinal symptoms are a class-specific effect of GLP-1 receptor agonists, regardless of which individual medicine is used.

For most users, these symptoms subside as the body becomes accustomed to the higher dose. If you want to know how this plays out in practice with a specific medicine, read more about the side effects of Ozempic in detail. Diet also plays a role: the diet recommended whilst taking GLP-1 medication can help alleviate nausea and stomach discomfort.

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

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

In addition, each medicine has its own specific considerations. In connection with Wegovy (semaglutide), an extremely rare eye condition (NAION) has been reported, in which the optic nerve is damaged. This occurs in approximately one in 10,000 people per year. A severe allergic reaction may also occur. And if the medicine is used in combination with insulin or certain diabetes medicines (SU derivatives), there is a higher risk of developing low blood sugar. With Saxenda (liraglutide), the skin may harden or thicken at the injection site (cutaneous amyloidosis). This is particularly likely to happen if the injection is always given in exactly the same place. Changing the injection site can help prevent this. A slight increase in heart rate, of around 3–5 beats per minute, has been reported with the use of Mounjaro (tirzepatide). According to Farmacotherapeutisch Kompas, these symptoms must always be reported to your doctor, even if they are rare.

What are the differences between GLP-1 medicines?

The medicines are very similar, but differ from one another 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 mild increase in heart rate. In other respects, the safety profile appears largely similar to that of the other medicines. Liraglutide (Saxenda) must be injected daily, whereas semaglutide (Wegovy) only needs to be administered once a week. This is because liraglutide is cleared from the body more quickly. It is also the only medicine where skin hardening may occur at the injection site. Hair loss has been observed slightly more frequently with semaglutide (around 2.5 per cent). Would you like to compare these medicines more broadly in terms of weight loss, dosage and effects? Then read our comparison of Ozempic, Wegovy, Mounjaro and Saxenda.

When should you contact your doctor whilst taking GLP-1 medication?

Contact your doctor immediately if you experience severe, persistent stomach pain, as this may indicate pancreatitis. Symptoms of dehydration, such as dizziness, a dry mouth or reduced urination, are also reasons why you should not delay. Sudden changes in vision, symptoms of a severe allergic reaction – such as swelling of the lips or difficulty breathing – and symptoms that significantly impair your ability to carry out daily activities are all reasons to contact your doctor or nurse. This list is not exhaustive: in any unclear situation, getting in touch is always the right choice.

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

Goodweigh provides ongoing medical monitoring whilst your dose is being increased. This monitoring is specifically designed to minimise side effects and, should they nevertheless occur, to detect them in good time and adjust your dose in consultation with your healthcare professional.

This means you don’t have to decide for yourself whether a symptom is normal or a sign that the dose needs adjusting. Would you like to find out more about what this support involves? Find out more about the Goodweigh weight loss programme.

The side effects of GLP-1 medicines are predictable and usually temporary

Most side effects of GLP-1 medicines are directly caused by the same mechanism of action that enables weight loss. They usually subside as your body gets used to the medicine, most often within the first few weeks or months of starting treatment or increasing the dose. With Goodweigh’s medical guidance, these side effects are monitored and, if necessary, managed so that you can safely progress towards your goal.