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Side effects

Injection-site reactions

A small red patch, an itch, a bruise or a little lump where the needle went in is common with any injection, and GLP-1 injections are no exception. Most settle within days. Rotating sites is what the labels ask for — partly for this reason, and partly to protect the skin over months of weekly injections.

By the Cafeity teamUpdated 3 min read

The short answer

Injection-site reactions — redness, itching, pain, bruising, swelling or a small lump — are listed on the GLP-1 labels: 6–8% on tirzepatide against 2% on placebo, 13.9% on liraglutide 3 mg against 10.5%, and 1.4% on semaglutide 2.4 mg against 1%.123 The labels ask you to rotate injection sites with each dose and not to inject into skin that is tender, bruised, red or hard, or that has pits, thickening or lumps. A site that is hot, spreading, very painful or oozing, or a reaction with swelling of the face or trouble breathing, needs prompt care.

Bar chart of injection-site reactions in the weight-management trials: Tirzepatide 8% versus 2% on placebo; Liraglutide 3 mg 13.9% versus 10.5% on placebo.
Share of trial participants who reported injection-site reactions, from each label. Not a head-to-head comparison.

How common they are

Injection-site reactions in placebo-controlled trials, from the current US prescribing information for each medicine. Rates from different medicines' trials are not directly comparable.
Medicine (trial population)PlaceboMedicine
Tirzepatide weekly injection (adults with obesity or overweight)2%6% (5 mg), 8% (10 mg), 8% (15 mg)
Liraglutide 3 mg daily injection (adults with overweight or obesity)10.5%13.9%
Semaglutide 2.4 mg weekly injection (adults with obesity or overweight)1%1.4% (label text)

The tirzepatide label adds a detail: reactions were more frequent in people who developed antibodies to the medicine (11.3%) than in those who did not (1%).1 The liraglutide label lists redness, itching and rash at the site as the most common.2

Rotation, and skin to avoid

The labels are specific:31

  • Rotate injection sites with each dose. You may use the same body area, but choose a different spot within it.
  • Do not inject into skin that is tender, bruised, red or hard.
  • Do not inject where the skin has pits, is thickened, or has lumps.
  • Keep at least 2 inches (5 cm) from the belly button.

The tirzepatide instructions give the reason for rotating: it reduces the risk of lipodystrophy (pitted or thickened skin) and localised cutaneous amyloidosis (lumps) at injection sites.1 The printable rotation chart turns this into a routine.

Bruises and small lumps

A small bruise usually means the needle nicked a tiny blood vessel; the tirzepatide instructions say to press a cotton ball or gauze on the site and not to rub it.1 A small firm lump that fades over days is common. A lump that grows, stays for weeks, or keeps appearing at the same spot is worth showing to your prescriber — and is a reason to leave that area alone meanwhile.

When to contact your prescriber

Keeping a record of it

Cafeity records the site of every injection on a body map, so rotation is visible rather than remembered — and a note about a red patch or a lump stays attached to the injection that caused it.

Cafeity dose screen: an estimated medication-level curve labelled "Estimate based on published half-life. Not a measurement", the last dose, the injection site (stomach, lower left), a countdown to the next scheduled dose and a side-effect check-in.
The injection site, recorded with the dose.
Cafeity medication-level chart over seven days, labelled "Estimate based on published half-life. Not a measurement", with the last dose, the injection site (stomach, upper left), the next scheduled dose and a side-effect check-in.
The last site at a glance.

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Common questions

Is a red itchy spot after a GLP-1 injection normal?
Mild redness or itching is a common, listed reaction and usually settles within days.12 Spreading redness, heat, swelling or fever need a clinician.
Why do I get lumps where I inject?
Small lumps can follow any injection. Repeatedly using the same spot can cause thickened or lumpy skin, which is why the labels ask you to rotate.1
Does injecting into a bruise matter?
The labels say not to inject into skin that is tender, bruised, red or hard.3

Sources

  1. Tirzepatide injection for weight management and obstructive sleep apnoea — US prescribing information DailyMed, US National Library of Medicine, version published 2 September 2026
  2. Liraglutide 3 mg injection for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 15 June 2026
  3. Semaglutide injection and tablets for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 30 June 2026

Written by the Cafeity team from the sources listed here. Figures from prescribing information are quoted as the label states them; trial results are averages from those trials, not predictions for any one person. This page has not yet been reviewed by a clinician — see the editorial policy for how pages are researched and corrected.