Symptoms and Signs of Drug Allergy

Medical Author: John P. Cunha, DO, FACOEP
Medically Reviewed on 9/19/2022

Doctor's Notes on Drug Allergy

Any unintended effect of a drug such as a 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 the 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 include hives, itching, flushing, lip swelling, tongue swelling, or eye swelling.

Other symptoms may include

Symptoms of severe allergic reactions (anaphylaxis or anaphylactic shock) can be life-threatening and may include

What Is the Treatment for a Drug Allergy?

Treatment for drug allergies depends on the severity of the reaction. If you have what you think is an allergic reaction to a drug, stop taking the medication and contact your doctor right away. If the reaction is severe or if you have shortness of breath, facial swelling, throat swelling, or feel like passing out from an allergic drug reaction, CALL 911 immediately to go to an emergency department.

For severe reactions, the following medications are usually given right away to rapidly reverse symptoms:

  • Epinephrine (EpiPen, Auvi-Q)
    • This drug is given only in very severe reactions (anaphylaxis).
    • If you carry an epinephrine auto-injector for allergies, use it right away
  • Antihistamines, such as diphenhydramine (Benadryl)
    • This drug is given in intravenously (IV) or in a muscle to rapidly reverse the actions of histamine
    • Oral diphenhydramine is usually enough for a less severe reaction
  • Corticosteroids
    • Corticosteroids are usually given via IV at first for rapid reversal of the effects of the mediators
    • These drugs reduce swelling and many other symptoms of allergic reactions
    • It will probably be necessary to take an oral corticosteroid for several days after this

For less severe reactions oral medications may be given. For mild allergic drug reactions drugs, medications such as these may be used:

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