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Allergies Health Center

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Facts About Drug Allergies

  • Anybody can be allergic to any drug. That includes prescription medications and everyday medicines you can buy at the drug store. Some drugs are much more likely to trigger allergic reactions, like some antibiotics, seizure medications, and some pain relievers.
  • Symptoms can start right away or weeks later. Many drug allergy symptoms start within minutes -- or even seconds -- of taking a drug. Others may show up days or weeks after. That can make it harder for you and your doctor to figure out what caused the problem.
  • Symptoms can be mild or severe. Drug allergies are most likely to affect your skin, causing rash or hives. They can also cause problems with your nose, airways, ears, or lining of your stomach. For some people, they may be life-threatening.
  • A drug allergy is different from a drug reaction. Having a bad reaction to a drug is very common. It can be anything from a mild side effect (like upset stomach) to a serious problem.
    True drug allergies are different. When you have an allergy, your own immune system causes the problem. Your body mistakes something harmless -- pollen, pet dander, a medicine -- for a hazardous substance. Your immune system churns out special cells and chemcials to fight the allergen, causing swelling and other symptoms.
  • You can develop a drug allergy at any time. Even a drug you've been taking for years can trigger an allergic reaction.
  • You won't have an allergic reaction the first time you take a drug. When you first take a drug, your body just becomes sensitized to it. The problem starts the next time you take it. By then, your body is prepared. As soon as it senses the drug in your body, it sounds the alarm and your immune system attacks.
    It’s rare, but people can seem to have a reaction the first time they take a drug. They actually may have taken the drug – or a similar drug – and just not know it. Sometimes, being exposed to a similar chemical in cosmetics is enough to sensitize a person.
  • Some people have a greater risk of drug allergies. We don't know why people get drug allergies. Some things seem to increase the risk, like
    • Having other allergies, such as hay fever
    • Previous drug allergies
    • Family history of allergies
    • Having certain diseases, like Epstein Barr, leukemia, or HIV
    • Being a woman
  • Some drug allergies may get better. Some people may lose their sensitivity or reactivity to drug allergies over time without any treatment. Penicillin allergies get better over ten years if you aren't exposed to it again.
  • You can manage your drug allergy. It can be scary, and diagnosing it can be hard. But by working with your doctor, you can figure out your drug allergy and learn how to work around it.

WebMD Medical Reference

Reviewed by Stanley M. Fineman, MD, MBA on October 24, 2014

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