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What is drug (medication) allergy?
Many people have experienced side effects to a drug (medication), such as a headache, stomach upset or mild nausea. These types of unwanted reactions are often predictable, meaning they are known possible reactions to a medicine.
Some people can have an allergic reaction to a drug. Allergic reactions are different to side effects and occur when the body’s immune system sees the drug as harmful and reacts to it. In cases of true allergy the individual develops antibodies to particular medications just like someone might develop antibodies to particular food proteins such as peanut or egg. Although true drug allergies are not common, if you suspect you or someone you know may have a drug allergy, it is important to be diagnosed correctly so that you can be given appropriate treatment when you need it.
Diagnosis
It can be difficult to know whether symptoms are due to a true allergy or part of an illness. For example, a rash that appeared whilst you were taking the drug could be due to the condition being treated rather than a true allergy. Abdominal pain and vomiting may be a side effect of the drug.
If you think you have an allergy to a drug, speak to your GP. A record of your symptoms can be helpful. Helpful information to provide the GP includes:
- How long ago the reaction occurred
- How long after you took the drug you began experiencing symptoms
- Whether you’ve had this drug before
- How long the symptoms lasted
- The nature of the symptoms – how serious they were and whether you needed to go to hospital
- Whether you’ve had the drug again since the reaction
- Whether you have any photos of the reaction
If it is uncertain whether you have an allergy to a drug, your GP may refer you to an allergy specialist for skin prick tests or blood tests. You may need to be tested in a hospital allergy clinic to confirm whether or not you have a drug allergy. For more about seeing an allergy specialist click here.
Signs and symptoms of drug allergy
Allergic reactions to drugs can occur immediately (within one to six hours) or can be delayed (more than 24 hours after taking medication).
Immediate allergic reactions
Immediate allergic reactions to drugs occur within one to six hours after taking the medication. Allergic reactions to drugs can be mild, moderate or severe (anaphylaxis).
Signs and symptoms of an allergic reaction
Learn about the signs and symptoms of allergic reactions, and the difference between a mild or moderate reaction and a severe reaction (anaphylaxis).
Non-immediate (delayed) allergic reactions
Delayed reactions are not as common and can occur days to weeks after commencing a drug, and even persist for some time after you stop taking it. This can vary in severity.
According to ASCIA (Australasian Society of Clinical Immunology and Allergy), severe non-immediate rashes due to drugs are associated with fever, flu-like and other systemic symptoms, and can be life-threatening. These are called severe cutaneous adverse reactions (SCAR) and require urgent specialist care.
If you experience signs of a severe reaction after taking a medication, call triple zero (000) for an ambulance. If you have milder symptoms of a drug allergy, see your GP as soon as possible.
Management
If you are confirmed to have a true drug allergy, you should:
- avoid taking that drug
- always tell health professionals about your medication allergy even if you have told them about it before
- be given an ASCIA Action Plan For Drug (Medication) Allergy by your doctor and give a copy to other health professionals involved in your care
- keep a ASCIA Record for Drug (medication) Allergy
- carry or wear medical identification that says you have an allergy to a drug and includes the name of the drug
- ensure the drug allergy is clearly documented in your medical records, including with your GP, hospital, pharmacy and My Health Record. A health professional having access to an accurate record of your allergies can be lifesaving in an emergency.
NOTE: Doctors rarely prescribe an adrenaline injector for people with a medication allergy as it is much easier to avoid a medication than it is to avoid other allergens such as food or insects.
For further information
You can find more information on allergies to specific drugs (medications), including penicillin, aspirin, sulphonamide and chlorhexidine, at ASCIA (Australasian Society of Clinical Immunology and Allergy).
Related information
Types of allergies
Learn more about the different types of allergic disease including diagnosis, triggers and treatments and about allergic reactions.
Living with allergies
Learn more about daily life with allergies – including reading labels and ingredients, managing different environments and what to do if you or a loved one has an an allergic reaction.