Jabwise

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.

Signs the NHS listsA swollen throat or tongueA raised, itchy rashDifficulty breathing

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.

MedicineAllergic reactionsSevere reactions
MounjaroCommon (may affect up to 1 in 10 people)Mounjaro KwikPen patient leafletRare (may affect up to 1 in 1 000 people)Mounjaro KwikPen patient leaflet
Zepbound5% at each dose, against 3% on placeboSerious hypersensitivity reactions (e.g., anaphylaxis, angioedema) have been reported postmarketing with tirzepatide.Zepbound prescribing information
WegovyNot listedRare: may affect up to 1 in 1,000 peopleWegovy FlexTouch patient leaflet
OzempicUncommon (may affect up to 1 in 100 people)Ozempic patient leafletRare (may affect up to 1 in 1 000 people)Ozempic patient leaflet

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.

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.

Jabwise Record Dose Change: Mounjaro from 10mg to 12.5mg, with the date it started

Sources

General information, not medical advice. Follow your prescriber’s guidance.

Getting real advice

We’re not doctors. This page sums up what the NHS and the official medicine information say, and can’t tell you what’s right for your body: your prescriber’s instructions and the leaflet in your box come first. More in our terms.

  • Quoted from official sources, each one linked
  • Sources checked 12 October 2026
  • No dosing advice; your prescriber comes first