Conditions and symptoms
What Is an Allergic Reaction? Medicine Label Warnings
Allergic reaction · say it: uh-LER-jik ree-AK-shunAlso written: allergy, drug allergy, allergic response
Short answer
An allergic reaction is when the immune system overreacts to something harmless, such as a medicine or food, causing symptoms from a rash to swelling.
What it means
An allergic reaction happens when the immune system wrongly treats something, such as a medicine, food, pollen or insect sting, as a threat. Mild reactions include itching, hives or a rash. Severe reactions can involve swelling of the face, lips, tongue or throat, wheezing, trouble breathing, or feeling faint; these need emergency help straight away, as they can be anaphylaxis.
Almost every medicine label mentions allergic reactions, often under 'Do not use if you are allergic to...' or 'Stop use and ask a doctor if an allergic reaction occurs.' This is because any medicine, including its inactive ingredients, can cause one in a person who is sensitive. If you have had a reaction before, labels and pharmacists will ask you to avoid that medicine and sometimes related ones.
An allergic reaction is not the same as a side effect. Nausea from an antibiotic is usually a side effect, not an allergy. A rash, hives or swelling is more likely to be allergic. The difference matters, because a wrong 'allergy' label can stop you getting a useful medicine.
Where you may see it
- The 'Allergy alert' or 'Do not use' section of over-the-counter labels
- 'Contraindications' sections of prescribing information
- Allergy records in medical notes
📄 How it looks on a report
Stop use and ask a doctor if an allergic reaction occurs. Seek medical help right away.
🙅 What it does not mean
- A side effect such as nausea is not usually an allergy.
- Having taken a medicine safely before does not mean you can never react to it.
- An allergy to one medicine does not always mean you are allergic to the whole family; ask your doctor.
🗒️ Questions to ask your doctor
💊 Medicines whose labels mention “Allergic reaction”
Plain-English explanations of each medicine, from its official FDA label.
- Acetaminophen
A pain reliever and fever reducer
- Albendazole
an anthelmintic drug, a medicine used to treat infections caused by parasitic worms
- Albuterol
A bronchodilator (a medicine that opens the airways) of the beta-2 adrenergic type. The FDA class is not listed, so this description comes from the label's own wording.
- Alprazolam
a benzodiazepine, a type of central nervous system medicine
- Amitriptyline
An antidepressant of the tricyclic type
- Amoxicillin
a penicillin-class antibacterial medicine that works against bacteria
- Amoxicillin and Clavulanate Potassium
A penicillin-class antibacterial combined with a beta-lactamase inhibitor, as the label describes it
- Ampicillin Sodium
a penicillin-type antibacterial medicine
- Apixaban
A factor Xa inhibitor, a blood thinner medicine (anticoagulant)
- Aripiprazole
an atypical antipsychotic medicine
🔗 Read more from trusted sources
- “Allergic reaction” on MedlinePlus ↗
US National Library of Medicine
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