Medication Allergies


What is a drug allergy?

A drug allergy is a form of bad physical reaction to a medication. There are different forms of allergic reactions to drugs, including immediate and delayed hypersensitivity reactions.

Immediate reactions (anaphylaxis) occur when the drug enters the body. The medication triggers a response by the immune system, and creates specific IgE antibodies (proteins made by the immune system to fight the drug). This is called “sensitization.”

When the medication is taken again, the IgE antibodies release large amounts of the chemical histamine, which try to rid the drug from the body. During a delayed reaction, immune cells help to fight the drug.

Symptoms and Causes

Which drugs most often cause an allergic reaction?

The most common cause of drug allergies is penicillin and other antibiotics similar to penicillin. Other drugs that can cause reactions (that do not involve IgE antibodies) include:

  • Sulfa drugs
  • Anticonvulsants
  • Non-steroidal agents (like aspirin and ibuprofen)
  • Contrast dye
  • Chemotherapy drugs

What are the symptoms of drug allergy?

Symptoms of allergic reactions can range from mild itching to life-threatening conditions. Many drugs can also cause side effects or intolerances such as an upset stomach. These symptoms do not always indicate a true allergy to a drug.

During an allergic reaction, histamine and other chemicals can cause symptoms that include:

Symptoms of more serious reactions include:

  • Difficulty breathing
  • Blueness of the skin
  • Dizziness
  • Fainting
  • Drop in blood pressure

Diagnosis and Tests

How are drug allergies diagnosed?

Drug allergies are diagnosed by a careful review of the patient's medical history and symptoms by a physician. If an allergy to an antibiotic such as penicillin is suspected, your allergist may do a skin test to confirm the allergy.

However, skin testing is not available for all drugs and in some cases could be dangerous. In special cases, your allergist may recommend a “challenge” (taking the medication again under medical supervision).

Because of the potential risk associated with a reaction — if you have had a severe, life-threatening, allergic-type reaction to a particular drug — your doctor may recommend the use of an alternative, equally effective medication.

Management and Treatment

How are drug allergies treated?

The primary concern when treating drug allergies is relieving the symptoms:

  • Common symptoms such as rash, hives, and itching can often be controlled with antihistamines and occasionally corticosteroids.
  • For coughing and lung congestion, bronchodilators (inhalers) may be prescribed.
  • For more serious, anaphylactic symptoms (life-threatening reactions, including difficulty breathing or loss of consciousness) epinephrine (adrenaline) is usually injected.

Desensitization is occasionally used for treatment of drug allergy, particularly when no testing is available or feasible. This technique is designed to allow your body to temporarily tolerate allergy-causing agents as long as you continue to use the medication.

For example, during penicillin desensitization, small amounts of penicillin are injected periodically at increasingly larger levels until your immune system learns to tolerate the drug. Desensitization procedures are not a cure for drug allergy.

Living With

Living with drug allergies

If you have a drug allergy, always inform your healthcare provider before undergoing any type of treatment, including dental care or surgical procedures.

It is also a good idea to either wear jewelry (bracelet or necklace) or carry a card that identifies your drug allergy. In cases of emergency, this type of identification could save your life.

Last reviewed by a Cleveland Clinic medical professional on 06/15/2016.


  • American College of Allergy, Asthma and Immunology. Drug Allergies ( Accessed 6/15/2016.
  • American Academy of Allergy, Asthma and Immunology. Drug Allergy ( Accessed 6/15/2016.
  • Covar RA, Fleischer DM, Boguniewicz M. Chapter 38. Allergic Disorders. In: Hay, Jr. WW, Levin MJ, Deterding RR, Ross JJ, Sondheimer JM, eds.CURRENT Diagnosis & Treatment: Pediatrics. 21st ed. New York: McGraw-Hill; 2012.
  • Arroliga ME, Pien L. Penicillin allergy: consider trying penicillin again. Cleve Clin J Med 2003; 70: 313–8.

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