Drug allergies happen when your immune system fights against a medicine it incorrectly sees as a threat and causes an allergic reaction.¹ Up to 1 in 10 people in the UK have a drug allergy.²

If you think you’re allergic to a medicine, your GP can refer you to a specialist for testing. If you may be having a serious allergic reaction to a drug now, you should call 999 or go to A&E right away. 

A drug sensitivity happens when your body cannot tolerate the side effects of a medicine. It’s sometimes also called a drug intolerance.¹ This is not the same as a drug allergy. 

Side effects are also not the same as a drug allergy. They can get better with time, and it may be best for you to continue taking the medication if you have mild side effects. 

Check the patient information leaflet of the medicine you’re taking to see the most common side effects. 

You can be allergic to any medicine, whether it’s a prescription drug, an over-the-counter product, or a herbal medication. But some drugs are more likely to cause allergies than others.

Some of the most common drugs that cause allergic reactions are:

• Antibiotics like penicillin 
• Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and aspirin 
• Local anaesthetic 
• General anaesthetic 
• Medicines used for high blood pressure known as ACE inhibitors 
• Chemotherapy drugs 
• Medicines used to treat epilepsy.¹

The symptoms of drug allergies vary depending on what you’re allergic to and how severe your allergy is.  

Some of the most common symptoms are: 

• A rash 
• Itching, especially on the face and around the eyes 
• Swelling 
• Wheezing 
• Nausea and vomiting 
• Diarrhoea. ^{3, 1}

Sometimes people have more severe symptoms. Anaphylaxis is a severe allergic reaction that can be fatal if it’s not treated. There are other severe allergic reactions that can develop to certain drugs.¹ If you have symptoms of anaphylaxis or a severe allergic reaction, call 999. 

The main way you can manage a drug allergy is to avoid the drug you’re allergic to.1 Make sure to always let clinicians know you have a drug allergy when you’re getting medical treatment. There may be alternative medicines you can take that work in different ways and do not cause allergies.  

If there is no alternative treatment, you may be given allergen immunotherapy. This is a process where you are given a tiny amount of the drug you are allergic to under medical supervision, in slowly increasing doses.²