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Symptoms and Signs of Drug Allergy

Doctor's Notes on Drug Allergy

Any unintended effect of a drug such as drug allergy or drug intolerance is considered an adverse reaction. A drug allergy is an immune reaction to a drug while drug intolerance is an unwanted side effect of a drug that is not caused by the immune system or problems with metabolism of the drug. When the immune system overreacts, a drug is viewed as a chemical "invader," or antigen. This is called a hypersensitivity reaction.

Symptoms of drug allergies include skin symptoms including hives, itching, flushing, lip swelling, tongue swelling, or eye swelling. Other symptoms may include joint pain, joint swelling, fever, and swollen lymph nodes. Symptoms of severe allergic reactions (anaphylaxis or anaphylactic shock) can be life-threatening and may include hives, redness/flushing, swelling, sense of warmth, itching, chest tightness, cough, wheezing, vomiting, diarrhea, abdominal pain/cramping, lightheadedness or loss of consciousness due to low blood pressure ("shock"), and rapid or irregular heartbeat.

Medical Author: John P. Cunha, DO, FACOEP
Medically Reviewed on 3/21/2019


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.