Drug Allergies: How They Differ from Side Effects and Why to Write Them Down
November 5, 2026 · 2 min read
Not every reaction after taking medicine is an allergy. Learn the signs of a drug allergy, the danger signs that need urgent care, and the habits that stop it happening again.
Have you ever had itching or a rash after taking a medicine? Many people call it an allergy straight away. But not every reaction after a medicine is an allergy, and the difference matters.
An allergy is not the same as a side effect
According to MedlinePlus, from the United States National Library of Medicine, a drug allergy is a reaction of the immune system to a medicine. The first dose often causes no trouble, but later doses can trigger a reaction.
Most side effects of medicines are not allergies. Many people mistake an unpleasant but not serious side effect, such as nausea, for a drug allergy.
Medicines that often cause allergies
MedlinePlus gives some examples:
- Penicillin and related antibiotics.
- Sulfa medicines.
- Seizure medicines.
- Insulin, mainly from animal sources.
- Substances containing iodine, such as contrast dyes for x rays.
Signs of a drug allergy
- Hives.
- Itching of the skin or eyes.
- A skin rash.
- Swelling of the lips, tongue, or face.
- Wheezing.
Danger signs: anaphylaxis
Anaphylaxis is a severe, sudden allergic reaction. Signs can include trouble breathing with wheezing or a hoarse voice, dizziness or fainting, hives over many parts of the body, stomach pain or cramps, nausea, vomiting, diarrhoea, confusion, and a fast, pounding pulse.
This is an emergency. Go to the emergency department straight away, or in Indonesia call the 119 medical emergency service.
What to do
- If you seem to be reacting to a medicine, contact your doctor.
- Avoid the medicine that caused it, and similar medicines too.
- Make sure every health worker who treats you knows about the allergy, including dentists, hospital staff, and pharmacists.
Write down the name of the medicine, when you took it, and the reaction you had. Keep the note on your phone or in your wallet, so it is easy to show wherever you get treatment.
A Coapotek pharmacist can help check whether a new medicine belongs to the same group as one that has caused you an allergy.
Sources
- MedlinePlus, U.S. National Library of Medicine. Drug allergies, reviewed 20 January 2026.
- Ministry of Health of the Republic of Indonesia. Akses Darurat Medis 119 Kini Bisa Melalui SATUSEHAT Mobile (The 119 medical emergency service can now be reached through SATUSEHAT Mobile), 5 October 2024.