# Injection site reactions: what to write down.

By [Max HP](https://maxhp.me/about) · Updated 3 November 2026

An injection-site reaction can be a small red patch, a passing itch or a lump that lasts a few days. It can also be the first sign of something that needs urgent care. The difference is easier to describe when the details are written down at the time.

## What the labels list

The GLP-1 labels use a small vocabulary for what can happen where the needle goes in: redness, itching, swelling, induration (a firm area under the skin), irritation, rash and bruising. The trials counted these events and reported them at different rates for different medications. The numbers below are from the placebo-controlled trials described in each label, not from a general estimate.

| Medication | What the label reports |
|---|---|
| [Wegovy®](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b) | “4% of WEGOVY-treated patients and 1% of patients receiving placebo experienced injection site reactions (including injection site pruritus, erythema, inflammation, induration, and irritation).” |
| [Zepbound®](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b) | “In ZEPBOUND-treated patients in a pool of Study 1 and 2, injection site reactions were more frequent in those with anti-tirzepatide antibodies (11.3%) compared to those who did not develop anti-tirzepatide antibodies (1%).” |
| [Mounjaro®](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d2d7da5d-ad07-4228-955f-cf7e355c8cc0) | “In the pool of placebo-controlled trials in adults, injection site reactions were reported in 3.2% of MOUNJARO-treated patients compared to 0.4% of placebo-treated patients.” |
| [Trulicity®](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=463050bd-2b1c-40f5-b3c3-0a04bb433309) | “In the placebo-controlled studies in adults, injection-site reactions (e.g., injection-site rash, erythema) were reported in 0.5% of TRULICITY-treated patients and in 0.0% of placebo-treated patients.” |

Quoted from the current US prescribing information on DailyMed, read in November 2026. The rates come from different trials with different designs, so they are not a ranking. Your own experience can be different from a trial average.

## What a common reaction looks like

The labels describe local reactions: a patch of redness, an itch, a small swelling, a firm lump or a bruise around the puncture. Some appear within hours and fade over a day or two. Others, particularly a firm area, can take longer to settle. The labels list injection-site reactions among the most common adverse reactions for Zepbound®, and at lower rates for the other medications.

A reaction is not automatically a reason to stop. It is a reason to look, record and mention it. The useful question at an appointment is not “did it happen?” but “when, where, how big, how long, and did anything else come with it?” A photograph taken on the day can answer the size question better than a description from memory.

Two practical details are easy to miss. The first is whether the skin was clean and the needle new; the label’s Instructions for Use cover both. The second is whether the same spot was used recently. A site log makes the second question answerable without relying on memory.

It also helps to separate the reaction from the injection itself. A small bead of blood, a momentary sting or a tiny bruise is a needlestick event, not necessarily a drug reaction. A red patch that appears hours later, an itch that spreads or a firm lump that lasts for days is a different pattern. The labels’ lists describe the second kind. Writing down the timing is what lets you tell them apart.

If the same site reacts twice, the record shows it. If a new pen or a new technique produces a different reaction, the record shows that too. None of this replaces a clinical assessment. It makes the assessment more specific, which is the most a log can do.

Size is the detail people underestimate. “A big red patch” means different things to different people. Compare it with something consistent, such as a coin, or measure the longest edge in centimeters. A photograph with the same phone and the same lighting is an easy second record. If the reaction is spreading, the sequence of photographs is more informative than any single description, and it gives the appointment a timeline rather than a snapshot. The same is true of a reaction that fades: the date it disappeared is part of the history, and so is the date, time and exact site of the next dose. That is the pattern in one line.

## What to write down

- **When it started**: The date and roughly how long after the injection. “Two hours after” and “the next morning” are different patterns.

- **Where it was**: The site, not just the area. “Left lower abdomen, two fingers from the last spot” is more useful than “stomach.”

- **What it looked like**: Size, color, whether it was raised, whether it was warm, whether it itched or hurt. A photograph is a good second record.

- **How long it lasted**: Hours, days or longer. Note whether it faded completely or left a mark.

- **Anything else that day**: A new pen, a new pharmacy, a different injection technique, a missed dose. Context is what turns a list of symptoms into a history.

Max HP keeps a reaction beside the dose that caused it, so the site and the date stay together. The [symptom diary](https://maxhp.me/glp-1-symptom-diary) does the same on paper. Either way, the record is more useful than a memory of “one time it went red.”

## When a reaction is not local

Most injection-site reactions stay near the injection. The labels also warn about serious allergic reactions, which can affect the whole body. The Wegovy® Medication Guide lists the signs this way:

> “Stop using WEGOVY and get medical help right away, if you have any symptoms of a serious allergic reaction including: swelling of your face, lips, tongue or throat; severe rash or itching; very rapid heartbeat; problems breathing or swallowing; fainting or feeling dizzy.”

A reaction that is spreading, involves the face or throat, or comes with trouble breathing is not a wait-and-see event. If any of those signs appear, contact your prescriber, or get emergency help.

## Questions

**Are injection-site reactions common with GLP-1 medications?**

The labels report them at rates from less than 1% to about 11%, depending on the medication and the trial. The Zepbound® label reports a higher rate in people who developed anti-tirzepatide antibodies. The numbers are trial averages, not a prediction for one person.

**What is the difference between a local reaction and an allergic reaction?**

A local reaction stays around the injection site: redness, itch, swelling, a lump or a bruise. A serious allergic reaction can involve the face, lips, tongue or throat, breathing, heartbeat or fainting. The labels list those signs, and they need urgent care.

**Do I stop injecting if a site reacts?**

That is a decision for your prescriber or pharmacist. What the record can do is show the pattern: which site, how soon, how large and how long. Bring that to the conversation rather than deciding alone.

**Can I use a different site next time?**

The labels list the abdomen, thigh and upper arm, and most say to rotate. If a site is painful or reacting, another allowed site may be more comfortable. Your prescriber or pharmacist can confirm what is suitable for your medication.

## Sources

1. [Wegovy® (semaglutide) prescribing information and Medication Guide](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b)⁠, DailyMed. Revised June 2026. Read 3 November 2026.

2. [Zepbound® (tirzepatide) prescribing information](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b)⁠, DailyMed. Revised August 2026. Read 3 November 2026.

3. [Mounjaro® (tirzepatide) prescribing information](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d2d7da5d-ad07-4228-955f-cf7e355c8cc0)⁠, DailyMed. Revised August 2026. Read 3 November 2026.

4. [Trulicity® (dulaglutide) prescribing information](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=463050bd-2b1c-40f5-b3c3-0a04bb433309)⁠, DailyMed. Revised March 2026. Read 3 November 2026.

## Read more

- [Injection site rotation: what to record](https://maxhp.me/blog/glp-1-injection-site-rotation)

- [GLP-1 injection sites and rotation](https://maxhp.me/injection-sites)

- [Free printable symptom diary](https://maxhp.me/glp-1-symptom-diary)

- [What to track on a GLP-1](https://maxhp.me/blog/what-to-track-on-glp-1)

Coming soon to the App Store

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Canonical: https://maxhp.me/blog/glp-1-injection-site-reactions · Updated 2026-11-03