CompareTheJab guide
What to expect, how to manage common side effects, and which warning symptoms mean you should seek medical help.
Updated May 2026 UK-focused guide
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Overview
Most Wegovy side effects are digestive and usually improve
Wegovy, also known as semaglutide, is a weekly weight-management injection used in the UK. It has a well-established clinical trial background, but side effects are still an important part of the decision-making process.
The most common Wegovy side effects are gastrointestinal. These include nausea, diarrhoea, constipation, vomiting and abdominal pain. For many patients, these symptoms are most noticeable in the early weeks or after dose increases, then improve once the body adjusts.
Quick summary: most side effects are manageable, but serious symptoms such as severe persistent abdominal pain, allergic reaction symptoms, or concerning mood changes should be taken seriously and discussed with a qualified healthcare professional.
Slower stomach emptying
Semaglutide slows how quickly food leaves the stomach. This can increase fullness, nausea, reflux and bloating.
Changed gut movement
GLP-1 activity can alter how the intestines move food and fluid, which may lead to diarrhoea or constipation.
Reduced appetite
Lower food intake can contribute to fatigue, headaches, reduced protein intake and nutritional gaps if diet is not managed carefully.
Visual guide
Quick visual summary
A simple infographic summary to help readers understand the main points before reading the full comparison.
Reference table
Wegovy side effects at a glance
The table below summarises common and serious side effects discussed in the guide, including how often they were reported and when they may improve.
| Side effect | How common | When it may improve |
|---|---|---|
| Nausea | Up to 44% | Often peaks weeks 2 to 6 and improves on a stable dose |
| Diarrhoea | Around 30% | Often settles within 2 to 4 weeks at each dose level |
| Vomiting | Around 24% | Usually worst early on or after dose increases |
| Constipation | Around 24% | May need ongoing hydration, fibre and movement |
| Abdominal discomfort | Around 20% | Usually improves within weeks |
| Headache | Around 14% | Often linked to dehydration and lower intake |
| Fatigue | Around 11% | Often improves within 4 to 8 weeks |
| Acid reflux | Around 8% | May need dietary changes or pharmacist/GP support |
| Hair loss | Around 3% | Usually temporary and linked to rapid weight loss |
| Pancreatitis | Rare | Needs urgent medical assessment |
Very common effects
Nausea, diarrhoea, vomiting and constipation
1. Nausea
Nausea is the most common Wegovy side effect. It may come in waves and can be worse around injection day or after dose increases.
- Eat smaller meals more frequently.
- Prioritise protein first at each meal.
- Stop eating once comfortably full.
- Avoid fatty, fried, rich or heavily spiced foods.
- Avoid lying down for two to three hours after eating.
2. Diarrhoea
Loose stools are common in the early weeks and after dose increases. For many people, this improves as the gut adapts.
- Stay hydrated throughout the day.
- Replace fluids and electrolytes if symptoms are persistent.
- Reduce artificial sweeteners if they worsen symptoms.
- Seek advice if severe, bloody or lasting beyond a few weeks.
3. Vomiting
Vomiting can happen during the early adjustment period. If vomiting prevents you from keeping fluids down, speak to your prescriber.
- Do not re-administer a dose if you vomit after injecting.
- Continue the regular weekly schedule unless advised otherwise.
- Seek help if you cannot keep fluids down for more than 24 hours.
4. Constipation
Constipation may be more persistent than diarrhoea and often needs active management.
- Increase fluid intake.
- Keep fibre in your diet from vegetables, fruit, legumes and grains.
- Walk daily if possible.
- Ask a pharmacist about suitable options if constipation continues.
Patient support
Most side effects can be managed with the right support
Wegovy side effects are usually most noticeable during the early weeks and dose increases, so preparation and clinical guidance matter.
Common effects
Other side effects to understand
Abdominal discomfort
Cramping, bloating or mild upper abdominal discomfort can happen because of altered gut movement. Mild symptoms often improve, but severe persistent pain needs urgent assessment.
Headache
Headaches are often linked to dehydration, reduced food intake or diarrhoea. Hydration and regular small meals may help.
Fatigue
Tiredness may be linked to lower calorie and protein intake. Prioritising protein and hydration can help energy levels during the adjustment period.
Acid reflux
Slower stomach emptying can worsen reflux or heartburn. Avoid late meals, elevate the head of the bed and speak to a pharmacist or GP if persistent.
Dizziness
Dizziness may occur, especially if blood pressure falls. If you take blood pressure medication and feel persistently dizzy, contact your GP.
Hair loss
Hair loss is usually temporary and often linked to rapid weight loss, lower intake and nutritional stress rather than semaglutide directly.
Important difference
What makes Wegovy different from Mounjaro?
Similar digestive side effects
Wegovy and Mounjaro share a broadly similar gastrointestinal side effect profile because both affect GLP-1 pathways in the gut.
Individual tolerance varies. Some people tolerate one medicine better than the other, so prescriber guidance matters.
No Mounjaro-style contraceptive warning
Wegovy does not carry the same oral contraceptive pill interaction warning associated with Mounjaro.
If you use contraception, discuss your specific circumstances with a qualified prescriber or pharmacist.
Cardiovascular evidence
Wegovy has strong cardiovascular outcomes evidence in people with obesity and established cardiovascular disease.
Medication review may be needed
If weight, blood pressure or other health markers improve, existing medicines may need review by a clinician.
Serious warning signs: when to seek urgent help
Stop Wegovy and seek urgent medical advice if you experience severe, persistent upper abdominal pain, especially if it radiates to the back or is associated with nausea and vomiting.
- Severe persistent abdominal pain
- Pain spreading through to the back
- Vomiting with severe abdominal pain
- Symptoms of a severe allergic reaction
- Significant sudden mood or behaviour changes
Higher dose
The newer 7.2mg Wegovy dose
The higher-dose Wegovy option is not a starting dose. It is intended for patients who have already reached and tolerated the standard maintenance dose.
- Digestive side effects may be more pronounced during the transition.
- Skin sensory changes such as tingling or hypersensitivity may be reported more often.
- A fresh adjustment period of four to eight weeks may be needed.
- Suitability should always be reviewed by a prescriber.
Surgery note
Tell your surgical team
Because Wegovy slows gastric emptying, people taking it should tell their surgical and anaesthetic team before any procedure involving general anaesthesia or deep sedation.
Some clinicians may advise stopping before planned procedures, but this should be discussed with your surgeon, GP or prescriber.
Timeline
When do Wegovy side effects usually improve?
Weeks 1 to 4
Some patients notice little at the starter dose, while others begin to feel mild nausea, fullness or appetite changes.
Weeks 5 to 8
Digestive side effects may become more noticeable as the dose increases. This is often one of the more challenging stages.
Months 2 to 4
Symptoms may briefly return with each dose increase, but many patients find the pattern becomes more predictable.
Month 5 onward
Many patients report side effects as manageable or largely reduced once they are stable on a maintenance dose.
Hair loss timing
If it happens, hair loss may appear two to four months after starting and often improves within several months.
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FAQs
Keep reading
- Mounjaro and Wegovy: What to Expect
- Can You Drink Alcohol on Mounjaro or Wegovy? A UK Guide
- What to Eat on Mounjaro to Protect Your Muscle — A UK Dietitian’s Complete Guide
- Best Wegovy Providers UK 2026: Compared by Price, Support, and Clinical Quality
Compare today's prices: Mounjaro · Wegovy
Frequently asked questions
What are the most common Wegovy side effects?
The most common side effects are nausea, diarrhoea, vomiting, constipation and abdominal discomfort. These are usually linked to slower stomach emptying and changes in gut movement.
Does Wegovy cause hair loss?
Hair loss can happen, but it is usually temporary and often linked to rapid weight loss, reduced calorie intake and nutritional stress.
Does Wegovy affect the contraceptive pill?
Wegovy does not carry the same contraceptive pill interaction warning associated with Mounjaro. Speak to a prescriber or pharmacist for personal advice.
What should I do if I have severe abdominal pain?
Stop Wegovy and seek urgent medical assessment, especially if the pain is severe, persistent, in the upper abdomen, or radiates to the back.
Are Wegovy side effects worse than Mounjaro?
Both have similar gastrointestinal side effects, but individual experiences vary. Some patients tolerate one better than the other.
This article is for informational purposes only and does not constitute medical advice. CompareTheJab is an independent comparison website and is not a medical service. Always consult a qualified healthcare professional before starting, changing or stopping any medication.
Side effect information reflects guidance available in May 2026 and may change as guidance is updated. Some links on this website may be affiliate links. Editorial content should remain separate from commercial relationships.
Medically reviewed: May 2026. Next review due: November 2026.
