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Allergies 101: Drug Allergies and Drug Allergy Reactions

June 2, 2023

As a physician, it’s important to talk to my patients about drug allergies. Allergic reactions to medications can range from mild to severe, and sometimes even life-threatening.

It’s essential to identify if you have any known drug allergies, so we can avoid prescribing medications that may cause an allergic reaction.

If you have had a previous allergic reaction to a medication, it’s important to let your provider know before they prescribe any new medication.

They may need to prescribe an alternative medication or adjust the dosage to avoid a potential allergic reaction.

In some cases, we may need to perform an allergy test to determine the cause of your allergic reaction.

Remember, your safety is our top priority, and being transparent about your drug allergies is crucial to avoid any potential complications in your treatment.

Because not all patients react the same way to a given medication, it’s important to determine what is a non-allergic versus an allergic reaction and to understand and recognize the differences between the potential side effects of a drug, drug sensitivity, and symptoms of a drug allergy.

What is a Drug Allergy?

A drug allergy is the response of the immune system to a specific medication. Prescription, non-prescription, and herbal medications all have the potential to provoke an allergic reaction.

However, according to the Asthma and Allergy Foundation of America (AAFA), true drug allergies are rare. While reactions to medication are somewhat common, only about 5% to 10% of those reactions are due to an actual allergic reaction to that drug.

See below for additional details on signs and symptoms to look for when determining if what you’re experiencing is a true drug allergy.

Drug Allergy Side Effects, Sensitivities, and Symptoms

Every patient can have a different adverse reaction to any medication. Because responses are unique to each individual, it’s important to understand and recognize the differences between the potential side effects of a drug, drug sensitivities, and symptoms of a drug allergy. 

Woman looking dizzy grabbing her forehead with one hand and leaning to the wall with the other hand due to a drug allergy reaction
Drugs are a common cause of allergic reactions. While not all adverse reactions to medication are true pharmaceutical allergies, symptoms can still range from mild to life-threatening and even fatal.

Drug Allergy Side Effects

A side effect is a known and expected effect of a drug that is not the intended therapeutic outcome. For example, common side effects of antibiotics include:

  • Diarrhea
  • Dizziness
  • Rash
  • Nausea

Drug Allergy Sensitivity

Some patients may have sensitivities to medications, but sensitivities are not the same as having a drug allergy.

Drug sensitivity comes from the natural metabolism of medication, and it varies from person to person. Some people have a lower threshold to the effects of drugs than others, which causes them to experience the side effects to a greater degree.

Sensitivity to drugs can also produce symptoms similar to those present during an allergic reaction but tend to be milder. However, a reaction that stems from drug sensitivity does not trigger a response from the immune system.

Drug Allergy Symptoms

An allergic reaction triggers a response from the body’s immune system. In the instance of a drug allergy, the body views the specific medication as a threat and begins to produce numerous chemical mediators (including histamine) in response. This rise in mediator levels causes the body to develop allergy symptoms.

Symptoms of a drug allergy can include, but are not limited to:

  • Skin rash or hives
  • Itching
  • Wheezing
  • Swelling
  • Vomiting
  • Feeling dizzy or light-headed
  • Anaphylaxis

Drug allergy symptoms can also appear immediately or hours, days, or even weeks after taking the medication. Although in most cases, allergic reactions to drugs appear within minutes to hours, in some cases there may be a delay of days or even weeks before the onset of symptoms.

People who suffer from drug allergies may experience symptoms regardless of whether the medication comes in pill, liquid, topical products, inhaled products or injectable form and reactions can occur on any part of the body.

Medications that Cause Drug Allergies

Any drug has the potential to cause an allergy. But the American College of Allergy, Asthma, and Immunology (ACAAI) notes there are five groups of drugs that are more likely than others to trigger an allergy than others. They are:

  • Antibiotics containing sulfonamides
  • Anticonvulsants (seizure medications)
  • Aspirin, ibuprofen, naproxen, and other nonsteroidal anti-inflammatory drugs (NSAIDs)
  • Chemotherapy drugs
  • Penicillin and related antibiotics

All About Penicillin Allergy

Penicillin is the most commonly reported drug allergy. The Centers for Disease Control and Prevention (CDC) indicates that up to 10% of people in the United States report having an allergic reaction to a penicillin class antibiotic in their past. 

It is important to note, penicillin allergies may not be as prevalent as commonly believed.

Although, as indicated above, up to 10% of people report having a prior allergic reaction to a penicillin class antibiotic, the CDC reports that studies have shown that less than 1% of the population is truly allergic.

Symptoms of a penicillin allergy can include:

  • Hives
  • Swelling of tissue under the skin
  • Throat tightness
  • Wheezing
  • Coughing
  • Trouble breathing

Although it is less common, a more severe allergic reaction to penicillin is anaphylaxis. Per the ACAAI, anaphylaxis can occur suddenly and worsen quickly. 

Symptoms of anaphylaxis can present as:

  • Tightness in the chest and difficulty breathing
  • Swelling of the lips, tongue, throat, and nose
  • Dizziness, fainting, or loss of consciousness 

Fortunately, allergy skin testing is available to determine if you are truly allergic or no longer sensitive to penicillin family antibiotics.

Tips for Managing a Drug Allergy

While it is not uncommon for drug allergies to fade as our immune systems age, it’s important to always be in communication with your doctors about any previous drug allergy diagnosis.

 If you do have a drug allergy:

  • Ask about related drugs that you should avoid
  • Ask about alternatives to the drug that caused the adverse reaction/allergy
  • Wear an emergency medical alert bracelet or necklace that identifies your allergy

It’s also important to always keep a list of medications that you’re taking and make a note of any adverse reactions that you experience.

Medically Reviewed By: Juan Mas, MD
Reviewed on: April 26, 2023

Our team of writers, editors, and medical experts goes over each article carefully to make sure the information is correct and that only reliable sources are used.

We regularly check to see if the info in this article matches up with the latest scientific research and expert advice so that we can give you the most up-to-date information. See list of trusted resources here.

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