A drug allergy, or an allergic reaction to drugs, is an unintended bodily response to a medication.
Symptoms can vary from a mild rash to death.
An allergic reaction occurs when a person's immune system reacts to the presence of a foreign substance in the body. It is an attempt by the body to get rid of the substance. In the case of a drug reaction, this response is harmful, and sometimes causes serious symptoms. An allergic reaction does not usually occur the first time a person is exposed to the drug. It is only after the body learns to recognize the substance that an immune system reaction is triggered.