Drug Allergy

An abnormal reaction to a drug, most commonly an antibiotic

  • Age, gender, genetics, and lifestyle are not significant factors

Both over-the-counter and prescription drugs can cause various problems. Most symptoms, such as nausea or diarrhoea, are not allergies but side effects that can affect anyone taking the drug. A drug allergy occurs when the immune system produces an abnormal reaction to a specific drug. Often, the reactions are mild, but some can be life-threatening.

What are the causes?

A drug may provoke an allergic reaction the first time you use it. It is also possible to develop an allergic reaction to a drug that you have been taking for some time. In the latter case, your body will gradually become more and more sensitive to the drug. Allergic reactions may occur with any drug but are most common with antibiotics. Your doctor will ask you about any known allergies before prescribing drugs.

What are the symptoms?

An allergic reaction to a drug may give rise to the following symptoms:

  • Wheezing.

  • Swelling anywhere on the body, but typically affecting the face and throat (see Angioedema).

  • Nausea and diarrhoea.

  • An itchy rash consisting of red, raised areas and, occasionally, white lumps (see Urticaria).

If you develop these symptoms and suspect that they are due to a prescription or over-the-counter drug, contact your doctor at once before taking the next dose. Rarely, a drug allergy may lead to a severe and potentially fatal reaction called anaphylaxis.

What might be done?

If your doctor suspects that you are allergic to a particular drug, he or she will advise you to stop taking it and may prescribe an alternative. Usually, mild symptoms disappear without treatment within a few days of stopping the drug. Itchy rashes can be treated with over-the-counter products such as calamine lotion or oral antihistamines. A drug allergy is usually lifelong. It is therefore important to inform any doctor who treats you that you have an allergy to a certain drug. If the reaction was severe, you will be advised to carry a card or bracelet with you at all times to alert other people to your drug allergy in case you need emergency treatment.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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