A drug allergy is the abnormal reaction of your immune system to a medication. Any medication — over-the-counter, prescription or herbal — is capable of inducing a drug allergy. However, a drug allergy is more likely with certain medications.

A drug allergy is not the same as a drug side effect, a known possible reaction listed on a drug label. A drug allergy is also different from drug toxicity caused by an overdose of medication. There are many ways in which people can react to drugs and medicines but not all of these are allergy related, which can cause confusion. Some people are genuinely allergic to certain drugs, but this is quite rare. Most drug ‘reactions’ are due to the various issues described below.

What if I suffer from another allergy?

Some drugs, such as penicillin and some anaesthetics, vaccines and other injections used in, for example, X-ray techniques, are known to be more likely to cause allergic reactions. They are used more cautiously for allergic people. If you suffer a fairly severe adverse reaction to a drug, or a repeated reaction on different occasions, this will usually be considered to be an allergy. It is important that this should be recorded in your medical notes and you should not be given the drug again. In each group of drugs, there are some that are less likely to cause allergic reactions.