Mounjaro vs Wegovy Side Effects: UK Patient Information (2026)
Side-effect profile comparison for Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4mg) in the UK. Patient information, not medical advice. No prescription-medicine prices.
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- Source type
- Named public and provider sources
- Primary source
- MHRA Drug Safety Update: GLP-1 receptor agonists
- Reporting period
- 2026-05-12
- Last updated
- 2026-05-12
- Figure type
- Mixed sources
- Use
- Research and comparison only
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Important information for UK consumers. Mounjaro (tirzepatide) and Wegovy (semaglutide 2.4mg) are prescription-only medicines (POMs) in the UK. UK regulations restrict the advertising of prescription medicines to the public, so this article is general patient information about safety — it is not an advertisement, not an offer of sale, and not medical advice.
Common side effects
Both medicines share a broadly similar side-effect profile, dominated by gastrointestinal effects during dose escalation:
| Effect | Mounjaro | Wegovy |
|---|---|---|
| Nausea | Common | Common |
| Vomiting | Common | Common |
| Diarrhoea | Common | Common |
| Constipation | Common | Common |
| Abdominal pain | Common | Common |
| Injection-site reactions | Common | Common |
| Fatigue | Common | Common |
Less common, serious effects
| Effect | Notes |
|---|---|
| Pancreatitis | Reported in pharmacovigilance. Seek urgent medical advice for severe abdominal pain. |
| Gallbladder events | Including gallstones and inflammation. |
| Hypoglycaemia | More likely if used alongside insulin or sulfonylureas. |
| Diabetic retinopathy complications | Reported in semaglutide trials in patients with type 2 diabetes; discuss eye-screening with a prescriber. |
| Suicidal ideation and self-harm | The MHRA Drug Safety Update covers reports relating to GLP-1 receptor agonists. |
What to discuss with a UK prescriber
- Whether your clinical circumstances change the risk profile.
- How the dose escalation will be paced to manage tolerability.
- What monitoring will happen during treatment.
- What to do if a side effect occurs and how to report via the Yellow Card scheme.
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Please tell us via the corrections route.
Frequently asked questions
What side effects are most commonly reported with GLP-1 medicines?
Gastrointestinal effects (nausea, vomiting, diarrhoea, constipation) are the most commonly reported, particularly during dose escalation. Injection-site reactions are common. Less common but serious effects reported in pharmacovigilance include pancreatitis and gallbladder events. The MHRA Drug Safety Update is the authoritative UK reference.
How do I report a side effect in the UK?
Report any suspected side effect via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk. Reports can be submitted by patients, carers, or healthcare professionals.
Why does this article not show prices?
Mounjaro and Wegovy are prescription-only medicines (POMs) in the UK. UK Human Medicines Regulations 2012 prohibit advertising POMs to the public. TreatCompare does not display UK POM prices on consumer pages.
Sources & further reading
- MHRA Drug Safety Update: GLP-1 receptor agonists — UK pharmacovigilance and safety reporting for GLP-1 weight-management medicines.
- MHRA Yellow Card scheme — UK consumer-facing reporting scheme for suspected medicine side effects.
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