# Allergic reactions on a GLP-1

> Both NHS pages list an allergic reaction (anaphylaxis) as a possible serious side effect, with a swollen throat or tongue, a raised, itchy rash or difficulty breathing. Mounjaro’s, Wegovy’s and Ozempic’s leaflets call severe allergic reactions rare, up to 1 in 1,000 people, and say get immediate medical help.

Canonical: https://jabwise.app/guides/allergic-reactions. Sources checked 12 October 2026. General information, not medical advice: follow your prescriber.

## How common it is

Each leaflet’s own words for how common allergic and severe allergic reactions are, quoted as written. Wegovy’s lists only the severe kind.

- **Mounjaro**: Allergic reactions: "Common (may affect up to 1 in 10 people)" ([Mounjaro KwikPen patient leaflet](https://www.medicines.org.uk/emc/product/15481/pil)); Severe reactions: "Rare (may affect up to 1 in 1 000 people)" ([Mounjaro KwikPen patient leaflet](https://www.medicines.org.uk/emc/product/15481/pil))
- **Zepbound**: Allergic reactions: 5% at each dose, against 3% on placebo; Severe reactions: "Serious hypersensitivity reactions (e.g., anaphylaxis, angioedema) have been reported postmarketing with tirzepatide." ([Zepbound prescribing information](https://uspl.lilly.com/zepbound/zepbound.html))
- **Wegovy**: Allergic reactions: Not listed; Severe reactions: "Rare: may affect up to 1 in 1,000 people" ([Wegovy FlexTouch patient leaflet](https://www.medicines.org.uk/emc/product/13800/pil))
- **Ozempic**: Allergic reactions: "Uncommon (may affect up to 1 in 100 people)" ([Ozempic patient leaflet](https://www.medicines.org.uk/emc/product/9748/pil)); Severe reactions: "Rare (may affect up to 1 in 1 000 people)" ([Ozempic patient leaflet](https://www.medicines.org.uk/emc/product/9748/pil))

## What else they say

- **Immediate help**: The leaflets say get immediate medical help for breathing problems, or swelling of the lips, tongue or throat.
- **Zepbound’s signs**: Zepbound’s label also lists severe rash or itching, fainting or feeling dizzy, and a very rapid heartbeat among the signs.
- **Reacted before?**: The NHS says it may not be suitable if you’ve had an allergic reaction to semaglutide, tirzepatide or another GLP-1 agonist.
- **In the KwikPen**: Mounjaro’s KwikPen leaflet says each 0.6ml dose contains 5.4mg of benzyl alcohol, which may cause allergic reactions.

## Questions

### Is a rash a side effect of Mounjaro?

Mounjaro’s leaflet lists allergic reactions such as rash, itching and eczema as common, up to 1 in 10 people. Severe allergic reactions are rare, up to 1 in 1,000.

### Is a red, itchy patch where I inject an allergy?

Both NHS pages list itchy or red skin where you inject among common side effects, separately from a serious allergic reaction.

### What should I do if I think I’m reacting?

Mounjaro’s, Wegovy’s and Ozempic’s leaflets say get immediate medical help and tell your doctor. Zepbound’s label says stop using it and get medical help right away.

## In Jabwise: Dose changes

Know which brand and strength you were on. My Dose keeps your brand, dose and how often you take it. Record a change and the day it started, and History lists every one with its date.

## Getting real advice

- **A pharmacist, your doctor or NHS 111**: If you’re not sure how to use your medicine, or a side effect bothers you or won’t go away. NHS 111 if you think you might be having serious side effects, or you’ve used too much. [NHS: Semaglutide](https://www.nhs.uk/medicines/semaglutide/), [NHS: Tirzepatide](https://www.nhs.uk/medicines/tirzepatide/), [NHS 111 online](https://111.nhs.uk/)
- **Report a side effect**: Anyone can, not only doctors. [Yellow Card (UK)](https://yellowcard.mhra.gov.uk/), [MedWatch (US)](https://www.fda.gov/safety/medwatch-fda-safety-information-and-adverse-event-reporting-program)

## Sources

- [Mounjaro KwikPen patient leaflet](https://www.medicines.org.uk/emc/product/15481/pil)
- [Zepbound prescribing information](https://uspl.lilly.com/zepbound/zepbound.html)
- [Wegovy FlexTouch patient leaflet](https://www.medicines.org.uk/emc/product/13800/pil)
- [Ozempic patient leaflet](https://www.medicines.org.uk/emc/product/9748/pil)
- [NHS: Tirzepatide](https://www.nhs.uk/medicines/tirzepatide/)
- [NHS: Semaglutide](https://www.nhs.uk/medicines/semaglutide/)