Wegovy Side Effects: Common, Serious and How They're Managed

Most people who take Wegovy (semaglutide) experience some side effects, usually gastrointestinal: nausea, diarrhoea, vomiting, constipation and abdominal pain are listed as very common in the UK product information. These are typically mild to moderate, most noticeable when starting treatment and after each dose increase, and tend to ease over time. Serious side effects, such as pancreatitis and gallbladder problems, are much less common but important to recognise. This guide explains what to expect, how often side effects occur, how they are managed, and when to get help.

How side effect frequencies are described

UK medicine leaflets use standard categories to describe how often side effects occur:

These figures come from clinical trials and post-marketing reports. They tell you how often an effect was reported, not how likely it is to happen to you.

Side effects listed for Wegovy

The table below summarises side effects in the UK Wegovy product information at the time of writing. It is not a complete list; always read the leaflet that comes with your medicine.

Sources: UK Wegovy Patient Information Leaflet and SmPC. Categories can change as more data emerge.

For a parallel guide on tirzepatide, see Mounjaro side effects. For an overview of the medicine, see the Wegovy hub.

Gastrointestinal side effects

Why they happen

Semaglutide slows stomach emptying and acts on areas of the brainstem that process fullness and nausea. These effects help reduce appetite, but they also cause many of the common side effects. Our guide to how Wegovy works explains the mechanism.

What the trials found

In STEP 1, which enrolled nearly 2,000 adults without diabetes, gastrointestinal side effects were the most common adverse events. They were usually mild to moderate and temporary, and most often occurred during the 16-week dose-escalation period. About 4.5% of people on semaglutide stopped treatment because of gastrointestinal side effects, compared with 0.8% on placebo. The overall pattern was similar in the other STEP trials.

Nausea

Nausea is the most frequently reported side effect. It is often worst for a day or two after the weekly injection and after dose increases.

Practical tips that many people find helpful:

• Eat smaller meals and stop when you feel full.
• Eat slowly.
• Avoid rich, fatty, fried or very sugary foods.
• Avoid lying down straight after eating.
• Sip fluids regularly through the day.
• Try bland foods when nausea is strong.

See managing nausea on GLP-1 medication.

Vomiting

Vomiting is less common than nausea but is listed as very common. Occasional vomiting may settle, but persistent vomiting can lead to dehydration. Contact your prescriber if you cannot keep fluids down.

Diarrhoea

Diarrhoea is common, particularly early in treatment. Keep up fluid intake, and consider oral rehydration solutions if it is significant. See diarrhoea on GLP-1 medication.

Constipation

Constipation can persist longer than other gastrointestinal side effects because gut transit slows and people eat less food and fibre. Drinking enough fluid, gradually increasing fibre and staying active can help. A pharmacist can advise on suitable laxatives. See constipation on GLP-1 medication.

Indigestion, reflux and burping

Slower stomach emptying can cause heartburn, reflux, bloating and burping, sometimes with an unpleasant sulphur taste. Smaller meals, avoiding late meals and avoiding fizzy drinks may help. See burping, reflux and indigestion on GLP-1 medication.

Other common side effects

Headache, tiredness and dizziness

Headache and tiredness are listed as very common. They may be linked to eating less, dehydration or lower blood pressure as weight falls. Staying hydrated and eating regular, balanced meals may help. Dizziness can also occur; take care when standing up quickly, and tell your prescriber if you take blood pressure medicines, as these may need review as you lose weight.

Hair loss

Hair loss is listed as common, and the UK leaflet notes it is reported more often at 7.2mg. In STEP 1, it was reported by around 3% of people on semaglutide compared with about 1% on placebo, and more often by women. It is thought to be linked largely to rapid weight loss, a pattern called telogen effluvium, and usually recovers. See Mounjaro and hair loss, which covers the same mechanism.

Injection-site reactions

Redness, itching or bruising at the injection site can occur. Rotating sites between the abdomen, thighs and upper arms helps. See how to use the Wegovy FlexTouch pen.

Altered skin sensation (dysaesthesia)

The UK leaflet and the STEP UP trial report altered skin sensations, such as tingling, burning or unusual sensitivity of the skin, more often at the 7.2mg dose. These were generally mild. Tell your prescriber if this happens.

Low blood sugar in people with diabetes

Semaglutide rarely causes low blood sugar on its own. The risk is higher in people with type 2 diabetes who also take insulin or a sulfonylurea, and doses of those medicines may need to be reduced. See GLP-1 medication and type 2 diabetes.

Serious side effects

Acute pancreatitis

Pancreatitis is inflammation of the pancreas. It is listed as uncommon. Symptoms include severe, persistent pain in the upper abdomen, which may spread to the back, often with nausea and vomiting. If pancreatitis is suspected, semaglutide should be stopped and urgent assessment sought. People with a history of pancreatitis should discuss this with their prescriber before starting. See GLP-1 medication and pancreatitis.

Gallbladder problems

Gallstones are listed as common, and inflammation of the gallbladder as uncommon. Rapid weight loss increases the risk of gallstones, whatever the cause. Symptoms include pain in the upper right abdomen, fever, and yellowing of the skin or eyes. See GLP-1 medication and gallbladder problems.

Dehydration and kidney problems

Significant vomiting or diarrhoea can cause dehydration, which may affect kidney function, particularly in people with existing kidney disease. The UK leaflet emphasises drinking enough fluids. See hydration on GLP-1 medication.

Diabetic eye disease

In people with type 2 diabetes, rapid improvement in blood sugar has been associated with temporary worsening of diabetic retinopathy. People with diabetic eye disease should be monitored, and should report vision changes.

NAION: a rare eye condition

In June 2025, the European Medicines Agency's safety committee (PRAC) concluded that non-arteritic anterior ischaemic optic neuropathy (NAION), a condition that can cause sudden loss of vision in one eye, is a very rare side effect of semaglutide, affecting up to 1 in 10,000 people. Product information in Europe was updated, with advice to stop treatment if NAION is confirmed. Check the current UK leaflet for the latest wording, and seek urgent help for any sudden loss of vision.

Serious allergic reactions

Anaphylaxis and angioedema are rare. Signs include swelling of the face, lips, tongue or throat, difficulty breathing or swallowing, and a rapid heartbeat. Call 999 if this happens.

Aspiration during anaesthesia or sedation

Because food can remain in the stomach longer, there is a risk of inhaling stomach contents during general anaesthesia or deep sedation. Always tell the surgical team that you take Wegovy. See GLP-1 medication before surgery and anaesthesia.

Mood and mental health

Regulators, including the European Medicines Agency, have reviewed reports of suicidal thoughts in people taking GLP-1 medicines and have not found evidence of a causal link. Monitoring continues. Anyone who experiences low mood or thoughts of self-harm should seek help. See GLP-1 medication and mental health.

Pregnancy and contraception

Wegovy should not be used during pregnancy. The UK product information advises that people who could become pregnant use contraception, and that semaglutide should be stopped at least two months before a planned pregnancy because it takes time to leave the body. The MHRA has reminded patients and healthcare professionals of this. See GLP-1 medication, pregnancy and fertility.

When side effects happen: the timeline

How side effects are managed

Adjusting the dose schedule

The Wegovy dose increases every four weeks. If gastrointestinal side effects are significant, the UK SmPC advises considering delaying the next dose increase or lowering to the previous dose until symptoms improve. These decisions belong to your prescriber. See Wegovy doses explained.

Eating and drinking

Small, regular meals, adequate protein, gradual increases in fibre, and good hydration help many people tolerate treatment. See what to eat on GLP-1 medication and foods that can worsen GLP-1 side effects.

Over-the-counter remedies

A pharmacist can advise on remedies for constipation, indigestion or diarrhoea that are suitable alongside your other medicines. Some medicines need to be taken at specific times, and slower stomach emptying can affect how some oral medicines are absorbed. See GLP-1 medication interactions.

Reporting side effects

You can report suspected side effects to the MHRA through the Yellow Card scheme, online or via the Yellow Card app. Reports help regulators monitor medicine safety.

Factors that may affect side effects

Not everyone experiences side effects to the same degree. Factors that may make them more noticeable include:

• Dose increases. Side effects commonly flare in the days after each step up.
• Eating patterns. Large, rich or fatty meals, eating quickly and eating late in the evening are often linked to worse nausea and reflux.
• Alcohol. Alcohol can worsen nausea, reflux and dehydration. The same principles described in our guide to Mounjaro and alcohol apply to semaglutide.
• Dehydration. Not drinking enough can worsen headache, tiredness, dizziness and constipation.
• Missed doses. If several doses are missed, side effects can return when treatment resumes. Your prescriber may advise restarting at a lower dose after a longer break. See Wegovy doses explained.
• Other medicines and conditions. Existing gut conditions, some medicines that slow the gut, and diabetes medicines that lower blood sugar can all interact with side effects.

Wegovy compared with Mounjaro

Wegovy and Mounjaro (tirzepatide) have similar side effect profiles, with gastrointestinal effects the most common for both. In the head-to-head SURMOUNT-5 trial, gastrointestinal side effects were common in both groups and the rates of stopping because of side effects were broadly similar. Because SURMOUNT-5 was open-label and funded by the manufacturer of tirzepatide, and because individuals vary, it is not possible to predict which medicine any one person will tolerate better. Some people who cannot tolerate one medicine do better on the other, but switching is a decision for a prescriber. See Mounjaro vs Wegovy and switching from Mounjaro to Wegovy.

Side effects in adolescents

Wegovy is licensed for weight management in adolescents aged 12 and over with obesity. In the STEP TEENS trial, published in the New England Journal of Medicine in 2022, gastrointestinal side effects were again the most common. Treatment in this age group should be overseen by appropriate specialist services, with attention to growth, nutrition and mental health.

What happens to side effects when you stop

Because semaglutide has a half-life of about a week, it takes several weeks to leave the body. Gastrointestinal side effects usually fade over this period. Appetite also tends to return, and weight regain is common. Stopping should be planned with your prescriber, who can discuss support for maintaining changes. See Wegovy maintenance and stopping.

Common myths about Wegovy side effects

"If you get side effects, the medicine is working better." There is no clear evidence that people who have more side effects lose more weight. People without nausea also lost weight in the trials.

"Side effects mean you should stop." Most side effects are mild and temporary. Any decision to stop should be made with your prescriber, unless you have red-flag symptoms that need urgent help.

"Serious side effects are common." Serious side effects such as pancreatitis are uncommon. They are important to know about so that you can act quickly, not because most people will experience them.

"Ozempic face is a side effect of the medicine." Changes in facial appearance are related to fat loss from the face, which can happen with any significant weight loss. See facial changes and loose skin.

Questions to ask your prescriber

1. Which side effects should I expect, and which should prompt me to contact you?
2. Can my dose increase be delayed if side effects are difficult?
3. Do any of my other medicines need adjusting, particularly diabetes or blood pressure medicines?
4. Which over-the-counter remedies are suitable for me?
5. How do I contact you if I have problems between reviews?

Choosing a service with good follow-up

If you are treated privately, the provider should offer a way to discuss side effects with a clinician and adjust your plan. When comparing services, it is worth checking how follow-up is handled and whether it is included in the cost. Our provider comparison explains how regulated services differ, and our prices page sets out what affects cost.

When to speak to a professional

Contact your prescriber, GP or pharmacist if:

• Nausea, vomiting or diarrhoea lasts more than a few days or stops you eating normally.
• Constipation is severe or lasts more than a week despite simple measures.
• You feel dizzy or faint, especially on standing.
• You notice hair loss, changes in skin sensation, or other effects that concern you.
• You have diabetes and have frequent low blood sugar readings or changes in vision.
• You notice changes in mood.

Seek urgent medical help (NHS 111, or 999 / A&E in an emergency) if you have:

• Severe, persistent abdominal pain, which may spread to your back, with or without vomiting. This can be a sign of pancreatitis.
• Pain in the upper right abdomen, fever, or yellowing of the skin or eyes, which can suggest gallbladder problems.
• Persistent vomiting or diarrhoea with signs of dehydration, such as confusion, very dark urine or passing very little urine.
• Sudden loss or blurring of vision.
• Signs of a serious allergic reaction, such as swelling of the face, lips or throat, or difficulty breathing. Call 999.
• Thoughts of self-harm or suicide. Call 999, go to A&E, or contact Samaritans on 116 123.

Your prescriber is responsible for deciding whether to continue, adjust or stop treatment based on your side effects.