Safety & Side Effects

Wegovy Side Effects

Learn about Wegovy side effects, including nausea, fatigue, and digestive symptoms, plus what to expect as your dose increases.

Whether you are about to start Wegovy or trying to make sense of symptoms a few weeks in, this guide covers the side effects of Wegovy (semaglutide) reported in clinical trials and on the UK product licence — what is common, what is rare, what to watch for, and when to seek help. LetsLoseWeight is an independent comparison site; we do not prescribe medication. The information below is for context, not personal medical advice.

How to read side-effect frequencies

Side effects on UK and European medicines licences are grouped into standardised frequency bands.

Frequency Meaning
Very common Affects more than 1 in 10 people
Common Affects up to 1 in 10 people
Uncommon Affects up to 1 in 100 people
Rare Affects up to 1 in 1,000 people
Very rare Affects fewer than 1 in 10,000 people

These categories come from the Wegovy Summary of Product Characteristics on the EMC, which is the authoritative UK reference for Wegovy side effects. The figures are based on data from the STEP clinical trial programme and post-marketing surveillance.

Very common and common side effects

Most Wegovy side effects are gastrointestinal — affecting the digestive system — and most settle within a few weeks as the body adjusts to each new dose level.

Very common (more than 1 in 10)

  • Nausea — the most frequently reported side effect across the STEP trials. Most pronounced after starting and after each dose escalation.
  • Diarrhoea
  • Vomiting
  • Constipation
  • Headache — listed as very common in Wegovy specifically.
  • Abdominal pain
  • Fatigue or tiredness

Common (up to 1 in 10)

  • Indigestion (dyspepsia)
  • Burping
  • Reduced appetite — partly the intended action of the medicine.
  • Bloating or excessive wind
  • Heartburn (gastro-oesophageal reflux)
  • Dizziness
  • Hair loss
  • Injection-site reactions — redness, mild pain or itching where the injection was given. Rotating between abdomen, thigh and upper arm reduces this.
  • Gallstones (cholelithiasis) — listed as common with Wegovy specifically, slightly more frequent than in some other GLP-1 medicines.
  • Hypoglycaemia (low blood sugar) — when used alongside insulin or sulfonylureas in people with type 2 diabetes.

Uncommon and rare side effects

These happen to fewer people but some need prompt attention.

Uncommon (up to 1 in 100)

  • Acute pancreatitis — inflammation of the pancreas. Symptoms include severe upper-abdominal pain that may radiate to the back, often with persistent vomiting. If this happens, stop Wegovy and seek urgent medical attention.
  • Gallbladder inflammation (cholecystitis) — pain in the upper right abdomen, sometimes with nausea or jaundice.
  • Dehydration — secondary to severe vomiting or diarrhoea.
  • Acute kidney injury — usually in the context of dehydration.
  • Increased heart rate
  • Hypersensitivity reactions — including rash, itching and skin changes.
  • Diabetic retinopathy worsening — in people with type 2 diabetes, rapid improvements in blood sugar can sometimes worsen pre-existing eye disease.

Rare (up to 1 in 10,000)

  • Severe allergic reactions including anaphylaxis and angioedema — symptoms include rapid swelling of the face, lips, tongue or throat, breathing difficulty and a fast heartbeat. Call 999 or go to A&E immediately if these occur.

Boxed warning: thyroid C-cell tumours and MEN 2

In animal studies, semaglutide caused thyroid C-cell tumours, including medullary thyroid carcinoma (MTC). It is not known whether semaglutide causes the same in humans. Because of this:

  • Wegovy must not be used by anyone with a personal or family history of medullary thyroid carcinoma, or with multiple endocrine neoplasia syndrome type 2 (MEN 2).
  • Patients should report symptoms such as a lump or swelling in the neck, hoarseness, difficulty swallowing or shortness of breath to a clinician promptly.

This is one of the contraindications listed in the SmPC and is a reason a regulated UK prescriber will not issue a prescription. See our eligibility guide for the full list.

Side effects in pregnancy and breastfeeding

Wegovy is not licensed in pregnancy. Anyone who becomes pregnant while taking Wegovy should stop the medicine and contact their prescriber. Because semaglutide has a long half-life, the SmPC advises stopping at least two months before a planned pregnancy.

It is not licensed during breastfeeding. There are no adequate data on whether semaglutide passes into breast milk in humans, so the licence advises against use.

Side effects on hormonal contraception

Unlike Mounjaro, the Wegovy SmPC does not carry a specific warning about reduced absorption of oral contraceptives. However, severe vomiting or diarrhoea can affect the absorption of any oral medicine, including the combined pill. Anyone experiencing significant gastrointestinal side effects should treat it the same way they would any other illness affecting the pill — follow the advice in the contraceptive's patient information leaflet, and consider a barrier method until symptoms settle.

What to do if you have side effects

Most common side effects settle within a few weeks of starting or after each dose increase, and there are practical strategies that can help — see our reduce side effects guide for diet and lifestyle tips.

If side effects are severe or persistent, options to discuss with your prescriber include:

  • Pausing at the current dose for an additional 4 weeks before next step-up
  • Going back down a dose level to the previous tolerable step
  • Staying at 1.7mg as a long-term maintenance dose if 2.4mg cannot be tolerated — this is permitted in the SmPC, with slightly lower efficacy
  • Stopping treatment if symptoms do not settle

When to seek urgent medical help

Call 999 or go to A&E if you experience:

  • Severe upper-abdominal pain that radiates to the back, often with persistent vomiting (signs of pancreatitis)
  • Rapid swelling of the face, lips, tongue or throat, or breathing difficulty (signs of a severe allergic reaction)
  • Severe allergic skin reactions (large rash, blistering)

Contact your GP or NHS 111 for:

  • Severe or persistent vomiting or diarrhoea leading to inability to keep fluids down
  • Severe abdominal pain that does not settle
  • Yellow skin or whites of the eyes (jaundice)
  • Lump or swelling in the neck, hoarseness, or trouble swallowing
  • Significant changes in vision (especially if you have type 2 diabetes)

Where there is any doubt, seek advice — pharmacists and NHS 111 are quick routes to a clinical opinion.

Reporting side effects

In the UK, suspected side effects to any medicine — including Wegovy — can be reported through the MHRA Yellow Card scheme. Anyone can report: patients, parents, carers and healthcare professionals. Reports help the MHRA identify new safety issues and update prescribing guidance.

Wegovy carries a black triangle (▼) in the BNF and patient information leaflet, indicating it is under additional safety monitoring. While this monitoring is in place, patients are encouraged to report any suspected side effect, however minor.

Frequently asked questions

Do Wegovy side effects get better over time?
For most people, yes. Gastrointestinal side effects are usually most noticeable in the first 1–2 weeks after starting or stepping up a dose, and then settle. The 16-week dose-escalation schedule is specifically designed to give the body time to adjust at each step.

Can I drink alcohol on Wegovy?
Wegovy itself does not have a direct alcohol interaction listed in the SmPC, but alcohol can worsen nausea and gastrointestinal upset and may make symptoms harder to distinguish from side effects of the medicine. People with type 2 diabetes should be careful because alcohol can lower blood sugar.

Are Wegovy side effects worse than Mounjaro's?
The two medicines have broadly similar side-effect profiles — both are dominated by gastrointestinal symptoms — though the rates differ slightly. In the SURMOUNT-5 head-to-head trial, gastrointestinal side effects were broadly comparable, with some differences in severity at the highest doses (Aronne et al., NEJM 2025). Tolerance varies between individuals.

Can Wegovy affect mental health?
The MHRA, EMA and FDA have all reviewed reports of suicidal thoughts and self-harm in people taking GLP-1 receptor agonists. Reviews so far have not found a causal link, but a small risk cannot be definitively ruled out. Anyone experiencing low mood, suicidal thoughts or self-harm urges while on Wegovy should contact their GP, NHS 111 (option 2 for mental health), or the Samaritans (116 123) and discuss with their prescriber.

Will my hair really fall out?
Hair loss (alopecia) is a recognised side effect. It is usually temporary and often linked more to rapid weight loss than to the drug itself. Adequate protein intake and a steady weight-loss pace can help.

Next steps

Sources

This guide is for general information only and is not a substitute for professional medical advice. If you experience symptoms after taking Wegovy, talk to your prescriber, your GP, or call NHS 111.

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Wegovy Side Effects UK: Common, Serious, What to Do | LetsLoseWeight