How to Handle a GLP-1 Injection Site Reaction: What to Record and When to Call

A GLP-1 injection site reaction is reported on all five FDA labels this page cites: the Ozempic, Wegovy, Mounjaro, Zepbound and Saxenda prescribing information each report it from placebo-controlled trials. The numbers differ by product. The Ozempic (semaglutide, Novo Nordisk) prescribing information, revised May 2026, reports injection site reactions such as injection-site discomfort and erythema in 0.2% of Ozempic-treated patients. The Wegovy (semaglutide) label, revised June 2026, reports 1.4% of Wegovy-treated adults in the weight-reduction trials versus 1% on placebo, and lists pruritus, erythema, inflammation, induration and irritation. The Mounjaro (tirzepatide, Eli Lilly) label, revised August 2026, reports 3.2% versus 0.4% on placebo in the pooled placebo-controlled trials. The Zepbound (tirzepatide) label, also revised August 2026, lists injection site reactions in its Table 1 at 2% on placebo and 6% to 8% across the three Zepbound doses studied. The Saxenda (liraglutide, Novo Nordisk) label, revised June 2026, reports 13.9% versus 10.5% on placebo, with erythema, pruritus and rash at the site each reported by 1% to 2.5% of Saxenda-treated patients.

Two more label facts frame the whole procedure. Both Eli Lilly labels report that injection site reactions were more frequent in patients who developed anti-tirzepatide antibodies: 4.6% versus 0.7% on Mounjaro, and 11.3% versus 1% on Zepbound. And the Saxenda label states that rotating injection sites within the same region reduces the risk of cutaneous amyloidosis, while the Mounjaro and Zepbound vial Instructions for Use say the same about lipodystrophy and localized cutaneous amyloidosis.

None of that tells you what a particular red patch on your thigh means. It tells you that the event is expected to happen to some people, that the labels care about where it happens and how often, and that the useful thing you can do, short of a phone call, is to record it well. This page is the record-keeping procedure. It is not treatment advice; the only treatment sentence on it is "ask your pharmacist".

Before you decide whether what you see is worth a call, read what your own medication's label says about it. Each of the five prescribing information documents this page cites (Ozempic, Wegovy, Mounjaro, Zepbound and Saxenda) has an injection-site-reactions passage in Section 6.1, and the Medication Guide at the back lists the symptoms the manufacturer and the FDA consider serious. DailyMed hosts all of them free; the where-to-inject reference page on this site quotes the site and rotation text from each label if you want them side by side.

Read the paragraph for your product, not a neighbour's. The Wegovy text names five terms; the Zepbound Table 1 footnote names bruising, erythema, pruritus, pain and rash. Knowing the words the label uses makes the rest of the record faster to write and easier for a pharmacist to read back.

This step takes two minutes once, and it changes the character of everything that follows. You are no longer wondering whether redness at an injection site is "a thing"; you have read the sentence that says the manufacturer counted it in a trial.

Record three things: which site you used, the date and time of the injection, and which dose entry the reaction belongs to. If you already keep a rotation log, the site name is the same one you wrote there, spelled the same way. If you do not, the rotation how-to explains why fixed names such as "left abdomen" matter and how to set them up.

Attach the reaction to the dose, not to the calendar day you noticed it. A reaction that appears two days after an injection is still a fact about that injection, and a log that stores it beside the dose entry keeps that connection visible. A log that stores it on a separate page loses it by the second month.

In GLP-1 Tracker the site is part of the dose entry, and a note on that entry is where the reaction goes, so the site, the date and the reaction are one record rather than three. On paper, add a "site note" column next to the site column and leave it blank most weeks.

Describe the reaction in three fixed fields: size, colour and feel. For size, compare it to a coin or hold a ruler beside it; "about a coin" or "three centimetres across" are both fine as long as you use the same method next time. For colour, plain words work: pink, red, purple, yellowing. For feel, choose from a short list and stick to it: itchy, tender, warm, firm, raised, bruised.

Those plain words map cleanly onto the label vocabulary. The Wegovy label's pruritus is itching, erythema is redness, induration is firmness, and the Zepbound footnote's injection site bruising is bruising. You do not need the Latin, but you do need to use the same plain word every time, because the point of the record is comparison. "Red, coin-sized, itchy, not tender" written four weeks running is a pattern; four differently worded impressions are not.

Resist writing an explanation. The record is what you saw. Why it happened, and whether it matters, are questions for the pharmacist or prescriber who will read it.

Take one photograph of the site, in the same light each time, with something in frame for scale: a coin, a ruler, the cap of the pen. Daylight from a window is the most consistent light most people have; failing that, the same lamp in the same room. Phone cameras date the image automatically, which makes it the one part of the record that dates itself.

One photo per day the reaction persists is enough. The purpose is not documentation for its own sake; it is to settle the question "is it bigger than yesterday?" Two dated photos side by side answer that more reliably than a memory of yesterday.

Keep the photos in one place you can find in six weeks, whether that is a photo album named for the medication or the same notebook as your log. A photo you cannot locate at the appointment did not happen.

Write the date the reaction first appeared, and when it has cleared, go back and write that date too. Duration is the field the pharmacist or prescriber will ask for first, and it is the one people are least able to reconstruct: "a few days, maybe a week" is the usual answer, and it is nearly useless.

Count in days from the injection, not just calendar dates, because the same day of the dose cycle can look similar from week to week. "Appeared day 1, gone by day 4" is a description that can be compared across doses and across sites. If it has not cleared by the next injection, note that explicitly; it is a different observation from a reaction that resolves in between.

The closing date is the entry most often forgotten, because by the time the reaction has gone there is nothing to prompt you. Tie the check to the next dose: when you log the next injection, look at the previous entry and close it if it is done.

Before anything else in this list, check what you see against the serious allergic reaction symptoms the Medication Guides name. The Ozempic, Wegovy, Mounjaro, Zepbound and Saxenda Medication Guides all carry a version of the same list: swelling of the face, lips, tongue or throat; problems breathing or swallowing; severe rash or itching; fainting or feeling dizzy; very rapid heartbeat. For those symptoms the Medication Guides instruct patients to stop using the medication and get medical help right away. That instruction comes from the label, not from this page, and the log can wait until afterwards.

The prescribing information behind those guides is consistent. Section 5.8 of the Ozempic label, Section 5.7 of the Wegovy label and Section 5.4 of the Mounjaro label each state that serious hypersensitivity reactions such as anaphylaxis and angioedema have been reported. The Zepbound label adds trial figures: immediate hypersensitivity reactions within one day of dosing occurred in 2.1% of Zepbound-treated patients versus 0.4% on placebo, and the majority of hypersensitivity reactions in the trials were skin reactions such as rash and itching.

A local reaction at the injection site and a whole-body reaction are different entries, and the labels treat them differently. The record on this page is for the first kind. Anything on the Medication Guide list is not a logging problem; it is an urgent-care call, and the entry gets written later.

Before the next injection, read the reaction notes from the last several doses next to the site column. You are looking for one distinction: does the reaction follow a particular site, or does it follow every dose regardless of site? Those are two different observations, and the record is the only way to tell them apart, because memory reliably remembers the worst one and forgets the pattern.

The labels supply the other half of this step. The Wegovy single-dose pen Instructions for Use say not to inject into an area where the skin is tender, bruised, red or hard, and to avoid scars and stretch marks. The Mounjaro and Zepbound vial Instructions for Use say not to inject where the skin has pits, is thickened, has lumps, or is tender, bruised, scaly or hard, or into scars or damaged skin. Skin that is still tender, bruised, red or hard is, by those Instructions for Use, not skin to inject into; which site to use instead is a question for your prescriber or pharmacist, and the rotation order is what makes the answer easy to find.

If the pattern is consistent, whichever shape it takes, that is the observation to bring to the pharmacist or prescriber, with the dated notes and the photos. "Right thigh, three of the last four times, red and itchy for about three days" is the kind of sentence the record exists to produce.

A reaction log tells you where a reaction happened, when, what it looked like, how long it lasted, and whether it lines up with a site or with every dose. That is all it does, and it is enough to make the next conversation with a pharmacist or prescriber a short one.

It does not tell you whether a reaction is expected, whether it needs treatment, or what to put on it. The Medication Guides answer the urgent question with their serious-allergic-reaction list; everything below that threshold is a question for the pharmacist who dispensed the pen, who can see the product, the record and you. GLP-1 Tracker keeps the site with the dose and the note with both, free on iPhone; it records what you enter and interprets none of it, and it is not a medical device.