Is Skin Rash a Side Effect of Mounjaro? (October 2026)

01 · The core answer

Is a skin rash a side effect of Mounjaro?

Local skin reactions at the injection site are a recognised side effect. Mild redness, itching, a small bruise or a tender lump is common and normally settles within a few days.¹³ In the weight-management trials, injection-site reactions were reported by 8.0% of people taking tirzepatide, compared with 1.8% on placebo.² The UK patient leaflet also lists allergic reactions such as rash, itching or eczema as common side effects, which may affect up to 1 in 10 people.

A widespread rash, hives or itchy welts away from the injection site is a different question. Do not diagnose it yourself: any new rash that is spreading or unexplained is worth discussing with your prescriber. If you are unsure whether a reaction is local, our guide to the Mounjaro skin reaction pattern explains how to tell.

02 · Your next step

What should you do if you get a rash?

First, work out where it is. A small patch of redness around the injection spot is the expected, minor kind. A rash elsewhere, or one that appears alongside feeling generally unwell, deserves a call to your clinical team.

If you are still working out whether treatment suits you, our weight loss clinic overview covers how a prescriber assesses suitability, and you can see the Mounjaro pen and consultation details when you are ready.

03 · Injection-site reactions

Injection-site reactions in detail

Mild redness, itching, a small bruise or a tender lump at the injection site is common and normally settles within a few days.¹³ Rotating sites each week and letting the pen warm briefly out of the fridge reduces stinging.¹³

Contact your clinical team if a reaction is spreading, hot, very painful, or lasts more than a week.¹³ The guide to itchy skin on Mounjaro covers itching without a visible rash.

Side effects in general are most likely when starting treatment or moving up a dose, and for most people they ease within days to a few weeks as the body adjusts.¹

04 · Allergic reactions

Signs of a severe allergic reaction

Serious side effects are uncommon but need urgent attention. Get medical help straight away for signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing.¹

If a rash comes with any of those signs, do not wait to see whether it settles and do not take another dose. Get medical help straight away. A rash on its own, with none of these signs, is less urgent but still worth a conversation with your prescriber, particularly if it is widespread or keeps returning after doses.

Our wider guide on whether Mounjaro can cause skin rash sets out the same safety steps in more depth.

05 · Skin changes that are not rashes

Skin changes that are not a rash

Some skin changes are about weight loss rather than the drug. Loose skin and a thinner-looking face are what losing a significant amount of weight quickly can do, on any method including diet or surgery. Skin commonly adapts gradually after weight stabilises.

Temporary hair shedding is also recognised. It is linked to rapid weight loss itself rather than a direct drug effect, and for most people it settles as weight stabilises. If skin feels unusually sensitive, see Mounjaro side effect skin sensitivity. For lasting problems, our page on irreversible side effects of Mounjaro puts concerns in context.

06 · Reporting a reaction

Reporting a suspected side effect

You can report any suspected side effect through the MHRA Yellow Card scheme, even if you are not sure the medicine is the cause.¹⁹ This helps regulators monitor safety.

Tell your prescriber about any new symptom. If a dose is hard to tolerate, prescribers can hold the current dose longer before stepping up, so speak to your clinical team rather than pushing through severe symptoms.¹ Our prescribing team offers ongoing monthly reviews and side-effect support to people we supply.

07 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹