Four kinds of skin reaction in the label
The Wegovy® documents describe skin reactions under separate headings, and it helps to know which is which before reading the numbers. [1][2][3]
| Reaction | Source and population | Wegovy® | Placebo |
|---|---|---|---|
| Rash | US, adolescents 12 and older [1] | 3% | 0% |
| Hives (urticaria) | US, adolescents 12 and older [1] | 3% | 0% |
| Injection-site reactions (itching, redness, inflammation, hardening, irritation) | US, adults in weight-reduction trials [1] | 1.4% | 1% |
| Any allergic reaction, by antibody status | US, adults [1] | 16% with antibodies; 7% without | — |
| Anaphylaxis; angioedema | EU SmPC section 4.8 [2] | Rare (1 in 10,000 to 1 in 1,000) | — |
| Rash; hives; anaphylaxis; angioedema | US post-marketing reports [1] | Reported; no rate | — |
Allergy: what the warning says
Section 5.7 of the US label says serious hypersensitivity reactions, such as anaphylaxis and angioedema (swelling under the skin, often of the face or throat), have been reported with Wegovy®. If one happens, the label tells prescribers to stop Wegovy®, treat it promptly and monitor until it settles. Anyone who has had a serious allergic reaction to semaglutide or any ingredient must not use it. [1]
The label adds that these reactions have also occurred with other GLP-1 medicines, and that it is unknown whether people who reacted to another one are more likely to react to Wegovy®, so caution is advised. [1] The Canadian monograph lists anaphylaxis and angioedema among reactions seen in under 1% of trial participants. [3]
Teenagers and antibodies
In the 68-week adolescent trial, 133 teenagers received Wegovy® and 67 placebo. Rash and hives were each reported by 3% on Wegovy® and by no one on placebo. [1] The paediatric section notes that teenagers had greater incidences of rash and hives than adults on Wegovy®. [1] The trial was small, so these percentages represent a handful of people.
Some people develop antibodies to semaglutide. In the adult weight-reduction trials, allergic reactions occurred in 8 of 50 people with these antibodies (16%) and in 114 of 1,659 without them (7%). [1] The label does not say what type of allergic reactions these were, and antibody testing is not a routine part of care.
Redness where the needle goes in
Injection-site reactions are listed separately. In the adult trials they included itching, redness, inflammation, hardening and irritation at the site, and affected 1.4% of people on Wegovy® versus 1% on placebo. [1] The EU rates them as common. [2] The Canadian definition also includes hives and swelling at the injection site. [3]
The label asks for the injection site to be rotated with every dose, using the abdomen, thigh or upper arm. [1] A reaction that stays at the injection site is different from a rash that spreads across the body, and the difference is worth telling your prescriber.
Why skin can react
- Supported by the label: semaglutide can trigger hypersensitivity, including in people with antibodies to it; injection-site reactions are a local response to the injection. [1]
- Not a rash: dysesthesia, also in the label, is a change in how skin feels, such as burning, tingling or pain to the touch, without a visible rash. [1] The Wegovy® body aches page covers it.
- General: MedlinePlus explains that hives are usually caused by an allergic reaction to a drug or food, but infections and stress can also cause them. [5]
Common causes unrelated to Wegovy®
MedlinePlus lists contact dermatitis from soaps, detergents, cosmetics, dyes in clothing, latex and rubber, along with eczema, psoriasis, shingles, insect bites, viral illnesses and other medicines, as frequent causes of a rash. [4] Alcohol swabs, adhesive plasters and new skin products used around injection day are worth thinking about too.
A rash that started around the time of a new antibiotic, a new detergent or an infection may have nothing to do with the injection. Your clinician will want the full list.
Care at home for a mild rash
For a simple rash, MedlinePlus suggests avoiding scrubbing, using gentle cleansers and warm rather than hot water, patting the skin dry, leaving the area open to the air, and stopping any newly added cosmetics or lotions. [4] It mentions non-prescription anti-itch creams and oral antihistamines for itching; ask a pharmacist before using them, since they may not suit everyone or every other medicine. [4]
Home care is only for mild rashes. Do not stop or change any medicine on your own, MedlinePlus says, but contact your provider if you are taking a new medicine and develop a rash. [4]
Wegovy® is a registered trademark of Novo Nordisk A/S. PepLabo is not affiliated with or endorsed by Novo Nordisk.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Face, lip, tongue or throat swelling; difficulty breathing or swallowing; a very fast heartbeat; fainting | Stop Wegovy® and call emergency services (911 or local number) | Emergency | Medication Guide [1]; MedlinePlus [4] |
| Severe rash or itching | Stop Wegovy® and get medical help right away | Emergency | Medication Guide [1] |
| Rash with fever, joint pain or sore throat, or red streaks and tender swelling | Your provider | Today | MedlinePlus [4] |
| A mild rash or hives that began after starting Wegovy® | Your prescriber | Today | MedlinePlus [4]; label §5.7 [1] |
| Redness or itching that stays at the injection site | Mention at your next visit, or sooner if it spreads | At your next appointment | Label §6.1 [1] |
