Redness, Itching or Bruising Where You Inject Ozempic, Wegovy, Zepbound or Mounjaro: What the Labels Say

A red patch, some itching or a small bruise where you inject Zepbound, Mounjaro, Wegovy or Ozempic is a side effect the labels list. On Zepbound it affected 6 to 8% of people in the weight-loss trials, against 2% on placebo, and it is usually mild^[1,5]. A reaction that spreads, feels hot, oozes pus or comes with a fever needs a call to your doctor soon^[8,10]. Swelling of the face, lips, tongue or throat, or trouble breathing, is an emergency^[1,2,3,4,12].

Everything I quote about the medicines comes from their FDA labels (Prescribing Information, Medication Guide and Instructions for Use, on DailyMed) and the European product information. I do not explain how to inject or discuss doses: your doctor or nurse does that. For what these medicines are, see what GLP-1 medications are.

How often injection site reactions happen

“Injection site reaction” is an umbrella term: redness (erythema), itching (pruritus), pain, bruising, rash or hardened skin where the needle went in^[1,2,3,4,5].

There is no Zepbound in the EU: the tirzepatide authorized by the EMA, including for weight management, is Mounjaro^[5]. Its EU label reports 8.0% against 1.8% on placebo in the weight-management trials^[5] and rates injection site reactions as common (up to 1 in 10 people) for Mounjaro and Wegovy and uncommon (up to 1 in 100) for Ozempic^[5,6,7].

Two caveats. The Zepbound label itself warns that adverse reaction rates in the trials of one drug cannot be directly compared to rates in the trials of another^[1]. And placebo is injected too, so it causes reactions as well: what the drug adds is the difference.

One more detail from the Zepbound label: injection site reactions were more frequent in people who developed antibodies to tirzepatide (11.3%) than in those who did not (1%)^[1].

Local reaction or allergy: where the line is

The labels keep injection site reactions and hypersensitivity (allergic) reactions separate^[1,2,4]. The practical difference is where they show up. A patch limited to the injection spot is the first. Hives (raised, itchy welts that move around), rash or itching elsewhere on the body point to the second^[1,2,3,4,6].

If welts appear away from the injection site or get bigger each week, tell your doctor before your next dose. The Medication Guides say not to use these medicines if you have had a serious allergic reaction to the active ingredient or any of the ingredients^[1,2,3,4].

Serious allergic reaction: this is an emergency

Anaphylaxis (a severe, whole-body allergic reaction) and angioedema (rapid swelling under the skin) are listed for all four medicines. In the US labels they come from postmarketing reports^[1,2,3,4]; in the Zepbound trials, 0.1% of people had severe hypersensitivity reactions, against none on placebo^[1]. The EU leaflets class them as rare (may affect up to 1 in 1,000 people)^[5,6,7], although the EU Ozempic SmPC lists angioedema with frequency “not known” because it comes from postmarketing reports^[6].

The Medication Guides use the same words for all four: “Stop using [the medicine] and get medical help right away” if you have any symptoms of a serious allergic reaction, including^[1,2,3,4]:

• swelling of your face, lips, tongue or throat
• problems breathing or swallowing
• severe rash or itching
• fainting or feeling dizzy
• very rapid heartbeat

According to the NHS, anaphylaxis symptoms usually start within minutes^[12]. Call 911 or your local emergency number.

Signs of infection: warmth, spreading redness, pus or fever

These labels do not list injection site infection as a side effect, so the reference here is general guidance for any injection under the skin. MedlinePlus says some soreness is to be expected, and to contact your provider if you see signs of infection such as redness, swelling, red streaks and a fever^[8]. In cellulitis, a common bacterial skin infection, redness or swelling gets larger as the infection spreads, the skin feels warm and tight, and there may be fever with chills or drainage if pus builds up^[10].

Bruises: what they are and how long they last

A bruise is blood trapped under the skin. MedlinePlus explains that it forms when small blood vessels break without the skin breaking. Most last about two weeks, going from reddish to bluish-purple and greenish-yellow^[11].

The Zepbound label counts injection site bruising among injection site reactions^[1]. About a drop of blood on the skin after the injection, the Zepbound pen instructions say: “This is normal. Press a cotton ball or gauze over the injection site. Do not rub the injection site”^[1].

Lumps that last for weeks: what the labels say

A small lump that lasts a few days can be part of a local reaction: the Wegovy label includes induration (hardening)^[3]. Lumps, pits or thickened skin that stay for weeks are a different matter.

No semaglutide or tirzepatide label lists that as a side effect or gives it a frequency. The only mention I found is in the US vial instructions for Mounjaro and Zepbound: “Change (rotate) your injection site within the area you choose for each dose to reduce your risk of getting lipodystrophy (pits in skin or thickened skin) and localized cutaneous amyloidosis (skin with lumps) at the injection sites”, and “Do not inject where the skin has pits, is thickened, or has lumps” or “where the skin is tender, bruised, scaly or hard, or into scars or damaged skin”^[1,2]. The pen instructions and the EU documents do not say this.

For insulin, MedlinePlus says not to inject into a spot that is lumpy, firm or numb, and calls this a very common cause of insulin not working the way it should^[9]. That is guidance for insulin, not data on GLP-1 medicines. If a lump does not go away, show it to your nurse or doctor.

Where to inject: the three areas in the labels, and rotating

All four are injected under the skin of the stomach area, thigh or upper arm^[1,2,3,4]. On changing sites^[1,2,3,4]:

The Ozempic Prescribing Information asks providers to tell patients to use a different injection site each week when injecting in the same body region^[4]. The EU Mounjaro label adds that if you also inject insulin, it goes in a different injection site^[5].

Could I be allergic to something in the pen?

Besides the active ingredient, each solution contains inactive ingredients, listed at the end of each Medication Guide. The only one a leaflet flags for allergies is benzyl alcohol. The Zepbound and Mounjaro Medication Guides say “Benzyl alcohol, glycerin, and phenol are also inactive ingredients in the multi-dose vial and single-patient-use KwikPen”^[1,2], so the single-dose pens and vials do not contain it; Wegovy and Ozempic do not list benzyl alcohol^[3,4]. The EU Mounjaro KwikPen leaflet says “Benzyl alcohol may cause allergic reactions”, at 5.4 mg per 0.6 ml dose^[5].

What about nickel or latex? None of the labels, Medication Guides or EU leaflets I read mention either. If you have a known allergy, bring the ingredient list from your Medication Guide to your appointment.

When to call your doctor, in the labels’ own words

The Medication Guides close their side-effect sections with nearly the same sentence. Zepbound’s: “Talk to your healthcare provider if you have any side effect that bothers you or that does not go away”^[1]. A reaction that comes back every week or gets bigger fits that.

It helps to bring details: which site, when it started, how big it got, how many days it lasted, and a photo on day one and day three. You can log it in the symptom diary and prepare your questions with the doctor-visit checklist.

The Medication Guides add that you may report side effects to the FDA, by phone at 1-800-FDA-1088 or through MedWatch^[1,2,3,4,13].

Frequently asked questions

Is it normal to get a red welt where I injected?

The labels list it: on Zepbound, 6 to 8% of people in the weight-loss trials had one, against 2% on placebo, and most tirzepatide reactions were mild^[1,5]. If it spreads, feels hot, oozes or comes with a fever, call your doctor: those are signs of infection^[8,10].

My Zepbound injection site itches like crazy. Am I allergic?

Itching at the injection spot is a common form of local reaction^[1,5]. If the itch spreads or welts appear away from the site, talk to your doctor before your next dose.

Why do I get a bruise after my Ozempic shot?

The labels count bruising as an injection site reaction^[1,6]. According to MedlinePlus, most bruises last about two weeks^[11]. Ask your provider if you bruise for no reason or a bruise looks infected.

I have a hard lump on my stomach where I inject. What is it?

If it lasts a few days, it may be part of a local reaction. If it stays for weeks, show it to your nurse or doctor; no label for these medicines gives a frequency for that kind of lump.

Do I need to wipe my skin with alcohol before injecting?

It depends on the product, because the Instructions for Use differ. The Ozempic pen instructions say to choose your injection site and wipe the skin with an alcohol swab, then let it dry^[4]. The Wegovy single-dose pen instructions say to clean the injection site with an alcohol swab or soap and water and let the skin dry, and the Wegovy FlexTouch instructions also use an alcohol swab^[3]. The Zepbound and Mounjaro single-dose pen instructions only say to wash your hands. With their vials and KwikPen, the swab is for the vial’s rubber stopper or the pen’s red inner seal, and none of their steps mentions cleaning the skin^[1,2]. Follow the instructions that came with your product, and ask your pharmacist or nurse if you’re unsure. Where to inject is above.