Long-term medical weight loss
Side Effect – Injection Site Reaction
Injection Site Reaction: What it is, Symptoms & Treatment
Injection site reactions are relatively common with GLP-1 medications (such as Mounjaro and Wegovy) and are usually mild and manageable.
Why Injection Site Reactions Occur?
These medicines are given under the skin (subcutaneously), and the injection itself can cause temporary irritation. Additionally, these medications contain a small amount of benzyl alcohol, which can occasionally act as a skin irritant, contributing to redness, itching, or mild swelling at the injection site.
Common Local Reactions
- Redness or discolouration
- Mild pain or tenderness
- Swelling or firmness under the skin
- Itching or warmth
These usually appear within a few hours of injection and resolve within a few days.
How to Minimise Local Reactions?
- Rotate injection sites – Avoid using the same area repeatedly. Suitable sites include the abdomen, thigh, or upper arm
- Clean the area properly – Use an alcohol swab and allow the skin to dry completely before injecting
- Inject at room temperature – If stored in the fridge, allow the pen or vial to reach room temperature before use (about 15–30 minutes)
- Use proper technique – Inject slowly and avoid rubbing the area immediately after injection
- Apply a cool compress for 5–10 minutes if mild redness or swelling occurs
What to Do If a Reaction Occurs?
- For mild redness or swelling – Apply a cool compress and monitor.
- Itching: You may use a gentle moisturiser or a mild steroid cream like Hydrocortisone 1% if there is no broken skin. An antihistamine tablet like Loratadine or Cetirizine can be taken to reduce the itching and redness.
- Avoid injecting into the same area until fully healed.
When to Seek Urgent Medical Advice
Call 999 or go to your Nearest A&E Immediately if you experience:
- Severe pain, significant swelling, or a hard lump that persists
- Blistering, open sores, or signs of infection (increasing redness, warmth, pus, fever)
- Widespread rash, severe itching, or any signs of an allergic reaction (e.g. difficulty breathing, swelling of the face, lips, or throat)
Most local reactions are mild and can be managed easily at home, but persistent or severe symptoms should always be reviewed.
Important Safety Advice
It is important to use GLP-1 medications safely and in line with clinical guidance. Side effects can often be managed effectively when identified early and addressed appropriately.
Maintaining open communication with your provider is key to ensuring safe and effective treatment.
Remember:
- Do not ignore persistent or worsening symptoms
- Do not increase your dose without clinical advice
- If you have had a break in treatment, restarting at a lower dose may reduce side effects
- Ensure your GP is informed of any new or unusual symptoms
Additional support
If you are experiencing side effects or have any questions about your treatment, our clinical team is here to help.
If your symptoms are severe, worsening, or you feel they require urgent medical attention, please seek immediate advice from your GP, NHS 111, or attend your nearest A&E department if appropriate.
For all other queries:
- Book a free video consultation with one of our trained clinicians through our website. Appointments are available throughout the week, including daytime and evening sessions.
- Send us your question online using our form: https://forms.medicinemarketplace.com/251345635207050 A member of our clinical team will respond by email.
- Speak to us by phone by calling 0330 175 5747, and selecting option 3.
We are here to answer your questions and provide support throughout your treatment journey.
Written by: Uzma Dala MPharm (2238839)
Approved by: Shameela Adam MPharm (2070113)
