Definition and Overview

A drug allergy is any abnormal immune reaction to a certain type of medication or a certain ingredient found in a drug formulation. This is a fairly common condition, affecting over three million individuals in the United States alone.

Like other types of allergic reactions, a drug allergy affects the individual’s immune system, which wrongly recognizes the drug entering the body as a harmful foreign substance. The immune system proceeds to attack what it recognizes as an invader, in an effort to expel it from the body. This typically leads to the overproduction of histamine, an increase in body temperature, restriction of the throat, and visible swelling in different parts of the body.

While some people suffer from relatively mild symptoms, drug allergy can cause serious reactions that can threaten the life of the patient. Every kind of drug in the market—be it synthetic or herbal, available over the counter or by prescription—can cause symptoms.

It is important to note that drug allergy is different from side effects caused by certain drugs. More often than not, drug manufacturers include a list of possible side effects in their packaging. These side effects can occur even in people without drug allergies. This condition is also different from drug toxicity, which is caused by ingesting a significantly higher than the prescribed dosage of a certain drug.

There are different types of medication that can cause allergic reactions, including the following:

  • Anti-seizure drugs (e.g. carbamazepine and phenytoin)
  • Analgesics, commonly known as painkillers (e.g. morphine, codeine, ibuprofen, aspirin, and indomethacin)
  • Antibiotics (e.g. tetracycline, sulfa drugs, and penicillin)
  • Chemotherapy medication
  • Corticosteroid (usually comes in the form of lotions or creams)
  • AIDS or HIV medication
  • Medication containing bee pollen or echinacea
  • Drugs for treating autoimmune diseases including rheumatoid arthritis

Causes of Condition

The main cause of drug allergy is the overreaction of the patient’s immune system. As described above, the immune system of an individual with drug allergy treats certain types of medication as unwanted invaders and works very hard to expel it.

There are factors that can increase the chances of an individual to have drug allergies, including the following:

  • Genetic factors, meaning that close relatives, including the parents, are suffering or have suffered from asthma and other allergies
  • The patient has suffered from food allergies in the past, such as shellfish, eggs, or soybeans
  • The medication is delivered through a syringe, rather than taken orally
  • The patient receiving larger doses of a certain drug but not necessarily to the point of overdose
  • Repeated exposure to the specific medication or ingredient causing the allergic reaction

Key Symptoms

Signs and symptoms of a drug allergy can vary from individual to individual, and can occur in different parts of the body. Compared to other types of allergic reactions, drug allergies might take a couple of hours, even a couple of days, before the patient experiences the symptoms, which typically include the following:

  • Rashes (usually resembles rashes caused by measles)
  • Hives
  • Sudden sensitivity to sunlight. Also known as photoallergy, this symptom also often leads to itchy, scale-like rashes after being exposed to the sun.
  • Joints and muscle ache
  • Steven’s Johnson Syndrome (itchy round bumps on the skin, which might be accompanied by a swollen tongue or face)
  • Fever
  • Shortness of breath or wheezing
  • Dizziness or light-headedness
  • Fainting
  • Teary, itchy eyes
  • Runny nose
  • Coughing
  • Heaviness in the lungs or congestion

One of the more dangerous symptoms is anaphylaxis. Though rare, this reaction can trigger dysfunction in a number of vital systems in the body. Anaphylaxis has its own set of signs and symptoms, including the following:

  • A noticeable drop in blood pressure
  • A faint yet racing pulse
  • Trouble breathing, because the throat is tightening
  • Nausea
  • Vomiting
  • Stomach cramps
  • Seizures
  • Diarrhea

Drug allergy can also cause other conditions such as:

  • Anemia - The number of red blood cells is reduced, resulting in shortness of breath, irregular heartbeats, and feelings of fatigue.

  • Nephritis - This condition involves the inflammation of the kidneys, which can lead to noticeable swelling in different parts of the body, uncharacteristic moments of confusion, hematuria (presence of blood in the urine), and fever.

  • Serum sickness - Symptoms of this condition include rashes, inflammation in different parts of the body, nausea, pain in the joints, and fever.

Who to See and Types of Treatment Available

A drug allergy is not a condition that can be completely cured, but the symptoms that arise from it can be treated. The goal of the treatment is to relieve symptoms, instead of addressing the root cause of the allergy, which is the immune system.

Like in other types of allergic reactions, minor signs and symptoms such as itchiness (in the skin, throat, nose, or eyes), hives, and skin rashes can be managed by antihistamines.

Widening the airways can be achieved with bronchodilators, which will allow the patient to breathe properly.

In the event that the patient suffers from anaphylaxis, the doctor or emergency medical personnel can administer epinephrine to save the patient’s life.


  • FDA: "Avoiding Drug Interactions."
  • American Academy of Allergy Asthma & Immunology: "Medications and Drug Allergic Reactions: Tips to Remember."
  • Celik G, Pichler WJ, Adkinson NF Jr. Drug allergy. In: Adkinson NF Jr., Bochner BS, Burks AW, et al., eds. In:Middleton's Allergy Principles and Practice.
  • Grammer LC. Drug allergy. In: Goldman L, Schafer AI, eds.Goldman's Cecil Medicine
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