Learn More About Drug Allergies

Reviewed by Sabrina Felson, MD on August 25, 2020

Many medications can cause side effects, and certain ones can trigger allergies. In an allergic reaction, your immune system mistakenly creates a response against the drug. It makes chemicals -- like histamine, and lots of it -- to get the medicine out of your body.

What Are the Symptoms?

Warning signs of a drug allergy can range from mild to life-threatening. In an allergic reaction, your body's release of histamine can cause symptoms like:

A more severe reaction may include:

The most severe reaction is one that includes anaphylaxis, a serious, life-threatening response marked by swelling, hives, and lowered blood pressure. In some cases, a person goes into shock.

If you think you're having anaphylaxis symptoms, give yourself a shot of epinephrine immediately and call 911.

What Are Some Common Drug Allergies?

The most common one is to penicillin. Other antibiotics can also cause allergic reactions.

Other possible culprits include:

  • Sulfa drugs
  • Barbiturates
  • Anticonvulsants
  • Iodine, which is found in many X-ray contrast dyes

How Are Drug Allergies Diagnosed?

Your doctor will start by reviewing your medical history and symptoms. If they think you’re allergic to an antibiotic like penicillin, they may do a skin test to confirm it. But skin testing doesn’t work for all drugs, and in some cases it could be dangerous.

If you’ve had a life-threatening reaction to a medication, your doctor will just rule out that drug as a treatment option.

What's the Treatment?

Allergy symptoms like rashes, hives, and itching can often be controlled with antihistamines, and sometimes with corticosteroids.

In a few cases, desensitization is used. Your doctor would give you tiny amounts of the drug by mouth, by IV, or with a shot in increasing amounts until your immune system learns to tolerate the medicine.

If you're severely allergic to certain antibiotics, your doctor can usually find an unrelated antibiotic that is safe for you.

How Can I Be Prepared?

If you have a drug allergy, always let your doctor know before you get any type of treatment, including dental care. It’s also a good idea to wear a MedicAlert bracelet or pendant, or to carry a card that identifies your drug allergy. These items could save your life in an emergency.

WebMD Medical Reference



The American Academy of Allergy, Asthma & Immunology. 

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