GLP-1 injection site reactions explained

A review published September 3, 2026 in Clinics in Dermatology looked at what happens at the injection site, and on the skin more broadly, for people using GLP-1 receptor agonists such as tirzepatide and semaglutide. The authors, Danielle Elgindi of Ohio State University and Vesna Petronic-Rosic of Cook County Health in Chicago, pulled adverse event reports from the FDA's reporting system and found that skin and injection-site reactions were the third most frequently reported adverse event category across the drug class^[1].

How common are these reactions

The review combined three sources: published clinical trials, pharmacovigilance studies, and case reports, then layered on a direct extraction of adverse event reports for six GLP-1 receptor agonists (tirzepatide, semaglutide, liraglutide, exenatide, dulaglutide and lixisenatide) from the FDA Adverse Event Reporting System. The authors combined injection-site reports with skin-related reports into a single category to compare rates across drugs^[1].

Out of 442,567 total adverse event reports across the six drugs, 137,412 (31.0%) involved a skin or injection-site reaction. The rate varied a lot by drug. Exenatide had the highest share of skin and injection-site reports at 53.1%, followed by dulaglutide at 33.5% and tirzepatide at 32.6%. Liraglutide sat at 17.1%, semaglutide at 12.2%, and lixisenatide had the lowest share at 6.9%^[1]. The authors note this is a reporting pattern, not a measured incidence rate, a distinction covered below.

What the reactions look like

The review deliberately narrowed its scope to non-immunologic reactions, meaning it looked at local, mechanical and irritant effects of the injection itself rather than true allergic responses such as hypersensitivity or anaphylaxis, which the authors treat as a separate category with a different mechanism^[1]. That distinction matters for a reader trying to work out whether a reaction is a routine part of injecting a drug weekly, or a sign of an allergic response that needs urgent attention.

The most commonly reported problems were pain, bleeding, redness (erythema), bruising, a palpable mass, itching (pruritus) and swelling at the injection site^[1]. Less common but still documented reactions included dysesthesias (abnormal skin sensations such as tingling or burning), nodules, granulomatous reactions (small firm lumps that form when the immune system walls off material under the skin) and hyperhidrosis (excess sweating)^[1].

The pattern lines up with what is already in the prescribing information for individual drugs. The US label for Mounjaro (tirzepatide) reports injection site reactions in 3.2% of patients on the drug across placebo-controlled trials, versus 0.4% on placebo, and notes the rate rises to 4.6% in patients who develop anti-tirzepatide antibodies, compared with 0.7% in patients who do not^[2]. A single-drug label figure like that is a narrower, trial-controlled measurement than the FAERS-derived proportions above, and the two are not directly comparable, but they point the same direction: injection-site reactions are a real, if usually minor, part of using this drug class.

What this is not

It is not a true incidence rate. FAERS, now folded into the FDA's Adverse Event Monitoring System (AEMS), is a passive reporting database: anyone (patients, clinicians, manufacturers) can file a report, reports are not verified, duplicates happen, and the FDA itself says the data cannot be used to calculate how often an event actually occurs in people taking a drug^[3]. A drug prescribed to millions of people will generate more raw reports than a rarely used one, independent of how safe either drug actually is. That is almost certainly part of why exenatide and dulaglutide, both used less widely than semaglutide in recent years, show up with the highest reporting shares.

It is also not a signal that these reactions are dangerous as a rule. The review's own conclusion is that most reactions were mild to moderate and were managed with supportive care, without needing to stop treatment^[1]. The authors are explicit that the next step is prospective research designed to actually measure risk rates, mechanisms and the best way to manage these reactions, something the FAERS-based comparison in this review cannot do on its own.

Where this lands

For someone using tirzepatide, semaglutide or another drug in this class, the practical takeaway is modest: expect that some redness, mild pain, bruising or a small lump at the injection site is common and usually resolves on its own. Persistent swelling, a lump that grows or does not go away, or any reaction that comes with fever or spreading redness is worth a call to the prescribing clinician rather than something to wait out. See the tirzepatide regulation and safety page and the semaglutide overview for the fuller safety picture on each drug, including the adverse events documented in their randomised trials.

One more boundary worth naming. The FAERS and AEMS reporting systems only cover FDA-regulated drugs^[3], which means this review says nothing about grey-market vials sold online as "tirzepatide, research use only" or similar. Those products sit outside the FDA's approval and reporting framework entirely, so none of the reaction rates discussed here apply to them, and their own risk profile (purity, dosing accuracy, contamination) is a separate and largely undocumented question.

This article is educational and journalistic, not medical advice. It describes what a published review found in reported adverse event data. Decisions about starting, continuing or stopping a GLP-1 receptor agonist belong with a clinician who knows the full picture.