A drug allergy occurs when your immune system reacts abnormally to a medication. A number of drugs can cause a drug allergy, including prescription and over-the-counter medications. The most common signs of a drug allergy are hives, rash or fever. You can have an allergic reaction to a drug anytime you take it, even if it caused no reaction in the past.
Most drug-related symptoms are not a true drug allergy and don't involve the immune system. Drug allergy and nonallergic drug reactions are often confused because they can cause similar symptoms. Either type is called an adverse drug event and needs to be checked by a doctor. Some allergic and nonallergic drug reactions can be severe or life-threatening.
Many allergic reactions start within minutes of taking a drug. However, it's possible to develop an allergic reaction to a medication after you've been on it for up to several weeks.
Drug allergy symptoms include:
It's possible to have an allergic response to a drug that caused no problem in the past.
If you have an anaphylactic reaction to a drug, your immune system responds to the drug as a harmful invader. This causes the release of histamine and other chemicals that cause allergic symptoms. Your immune system then becomes keyed to react the same way if you take the drug again in the future. However, the immune system changes over time, and eventually it's possible your drug allergy may go away on its own.
When to see a doctor
Call your doctor if you have a reaction after you take a drug. Mild allergic reactions are usually treated by stopping the drug and substituting another. If possible, see your doctor when the allergic reaction is occurring. This will help identify the cause and make sure you get treatment if it's needed.
Seek emergency treatment for signs of a severe reaction or suspected anaphylaxis after taking a medication. Signs and symptoms of an emergency drug reaction include:
A drug allergy occurs when your immune system mistakenly identifies a drug as if it were a harmful substance instead of a helpful remedy. Your immune system then reacts to the medication. Chemicals released by this reaction cause the signs and symptoms associated with an allergic reaction.
It isn't clear why some people develop drug allergies or other adverse drug reactions while others don't. Inherited traits may play a role, along with environmental factors and taking a number of medications over time.
Nonallergic adverse reactions
Some examples of drugs that commonly cause nonallergic reactions include:
While anyone can have an allergic or nonallergic reaction to a drug, a few factors can increase your risk. These include:
Those who have a greater risk of developing a more severe reaction to medications include people with:
Complications of serious drug reactions can include:
Drug reactions can result in:
Preparing for your appointment
If you have a reaction to a drug, see your doctor as soon as possible. If the reaction is severe, get emergency help. If you had a past reaction and are now following up with your doctor, here are some things you can do to make the most of your appointment.
What to expect from your doctor
Tests and diagnosis
If you have an unexpected drug reaction, steps that your doctor may take to diagnose the source of the problem include:
Treatments and drugs
Drug allergy treatment generally involves stopping the medication. You may also need medications to ease symptoms or, in the case of a serious reaction, emergency care.
If you have a history of a possible drug allergy, a skin test may help find out for certain. Tests for penicillin allergy are generally more reliable than are skin tests for allergies to other drugs.
Once you know you have a drug allergy, you'll need to avoid that drug and related drugs. Tell all of your health care providers, including your dentist, about your drug allergy. In case you're in an accident, you may want to wear a medical alert ID bracelet so that emergency workers will know about your allergy. In addition, you may want to carry a portable epinephrine injection (EpiPen, EpiPen Jr, Twinject) with you.
Last Updated: 2011-10-14
© 1998-2014 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "Mayo Clinic Health Information," "Reliable information for a healthier life" and the triple-shield Mayo logo are trademarks of Mayo Foundation for Medical Education and Research.
Terms and conditions of use