Marks at the injection site are uncommon, and when they happen they are usually minor. In the weight-management trials, 1.4% of people taking semaglutide reported a reaction at the site, against 1% of people injecting placebo. The short list of things that warrant a call is at the bottom of this page, and it is short on purpose.
Induration: the label's word for a firm or hardened patch of skin, as distinct from a bruise, which is bleeding under the skin, or a lump, which is a raised swelling. The three get used interchangeably in conversation and mean different things on a label.
How common is any mark at all?
Uncommon, and barely more common than injecting nothing.
The US semaglutide label records injection site reactions in 1.4% of treated adults and 1% of adults receiving placebo, grouping together injection site itching, redness, inflammation, hardening and irritation (label).
Tirzepatide groups the term more broadly — adding bruising, pain and rash — and its injection site reactions sit among the reactions reported in 5% or more of patients (label). A wider net catches more, so the two numbers should not be read against each other as though one medicine were gentler.
One further detail from the tirzepatide label, which is useful if a pattern develops over months rather than weeks: injection site reactions were more frequent in patients who developed antibodies to the medicine, at 11.3% (label).
How long does a mark last?
Nobody has published it.
No source located in preparing this article reports how long an injection site mark from these medicines takes to settle. That absence is worth stating rather than papering over, because an invented figure fails in both directions: a reader whose mark clears in a day wonders what went right, and a reader whose mark is still there on day five thinks something is wrong when it may not be.
What is more useful than a number of days is the direction of travel. A mark that is fading, shrinking, or becoming less tender is behaving the way a minor injury behaves, however long it has been there. A mark that is spreading, getting more painful, or getting warmer is not, however recent it is. That distinction is the one to act on, and it does not require you to know the average.
Bruises specifically
A bruise is bleeding under the skin from a small vessel that happened to be where the needle went. It is largely luck rather than technique.
The best evidence on reducing it comes from elsewhere in medicine. In research on other injected medicines rather than GLP-1 specifically, pooling five randomised trials and 503 participants, a slower injection may have reduced bruise size at 48 hours — an outcome the reviewers rated very low certainty, having downgraded every outcome in the review to low or very low (Cochrane 2021).
A smaller single trial, again in research on other injected medicines rather than GLP-1 specifically, found that a slower injection combined with dry cold applied before and after reduced pain and bruising (Şendir 2015). Both of its slower-injection groups differed from the control, so the trial does not isolate what the cold contributed on its own.
Neither of those is an instruction from us. With a pen, the injection duration is set by the device and the hold your leaflet specifies, not by you. And the cold finding rests on one small study in a different medicine — enough to mention, not enough for a clinic to tell you to do it. If you want to change something about your technique, that conversation belongs with your prescriber or pharmacist, who can see the pen you actually have.
Lumps, and why rotation is on the label
Both labels instruct rotating the injection site with each dose (semaglutide, tirzepatide). That instruction is not decorative, and the reason usually given comes from the insulin literature.
In research on other injected medicines rather than GLP-1 specifically — insulin-treated diabetes — incorrect site rotation and needle reuse are the most substantial risk factors for lipohypertrophy, a firm fatty thickening that builds where injections are repeatedly given in the same spot (Mader 2026). That analysis's senior author declares advisory-board and speaker relationships with several manufacturers.
That last sentence is doing real work here. Whether lipohypertrophy occurs with weekly GLP-1 dosing has not been established, and it would be easy to imply that it does. Insulin is injected several times a day; a weekly medicine puts far fewer injections into the same tissue. What can be said is that rotation is a label instruction for both medicines, that the mechanism behind the instruction is well described in a different drug class, and that following it costs nothing.
The site lists themselves, and the clearance from the navel, are in injection sites, storage and travel.
When a mark is a reason to call
Short list, and none of it is subtle.
- Redness that is spreading rather than settling
- Pain that is increasing rather than fading over days
- Warmth around the site, or fever
- Pus, or a discharge from the site
- A hard lump that keeps growing, or one that does not change at all over weeks
- Any reaction that involves more than the site — a rash elsewhere, swelling of the face or throat, or difficulty breathing
The last one is not really an injection-site question. Anything that goes beyond the skin at the spot belongs with the wider list in red flags on GLP-1, which covers the systemic warnings — the ones about the rest of the body rather than the puncture.
What this page does not cover
This page is about the skin where the needle went. It is not about nausea, abdominal pain, gallbladder symptoms or anything else the medicine does elsewhere, all of which are covered in GLP-1 side effects and the red-flag page above.
If you are still deciding whether to start and this page found you first, your first GLP-1 injection is the more useful place to begin.
Common questions
Is a bruise after the injection normal?
Marks at the site are uncommon and usually minor. In the weight-management trials, 1.4% of people on semaglutide reported an injection site reaction against 1% of those injecting placebo (label).
How long does an injection mark last?
No source we could find publishes a duration for GLP-1 injection marks. What matters more than the number of days is the direction of travel: a mark that is settling is reassuring, and one that is spreading or becoming more painful is worth a call.
Why does the label say to rotate sites?
Both medicines instruct rotating the injection site with each dose (semaglutide, tirzepatide). In research on other injected medicines rather than GLP-1 specifically — insulin users — incorrect rotation and needle reuse are the biggest risk factors for a firm fatty thickening called lipohypertrophy (Mader 2026).
When should I call someone about an injection site?
If redness is spreading rather than settling, if pain is increasing rather than fading, or if there is warmth, fever or pus. Anything that goes beyond the site itself — breathing, swelling of the face or throat, severe abdominal pain — belongs with the wider red-flag list rather than this page.
Does injecting more slowly reduce bruising?
It may, slightly. Pooled trials in research on other injected medicines rather than GLP-1 specifically found a possible reduction in bruise size two days later, across five trials and 503 people, an outcome the reviewers rated very low certainty (Cochrane 2021).