Like HowStuffWorks on Facebook!

Understanding Drug Allergies

Although people experience all kinds of reactions to medications, these are usually side effects of the drug (which you'll usually find listed and described in the patient information insert) rather than allergic reactions.

An unexpected allergic reaction to a drug is rare, but the symptoms can be severe, ranging from skin rashes and hives to fever and anaphylaxis, a severe and life-threatening reaction that includes swelling of the mouth and tongue, rapid heartbeat, difficulty breathing, a drastic drop in blood pressure, unconsciousness, and even death. This article will help you to better understand the nature of drug allergies.

Which Drugs Can Cause Allergies?

Drugs infamous for causing allergic reactions are some of the same drugs made famous for saving countless lives, most notably penicillin and sulfa drugs. Other drugs known to cause allergic reactions include barbiturates (rare), anticonvulsants, Novocain and other local anesthetics (very rare), and insulin, especially insulin derived from animal sources. Aspirin and aspirinlike drugs are also a common cause of allergic reactions and are known to trigger asthma attacks, especially in children.

Risk for Allergic Reaction

Are you at risk for having an allergic reaction to a drug? The following will help you decide:

  • Family history. Is anyone in your family allergic to any drugs? If so, you may have inherited the allergic tendency.
  • How long have you taken a drug? You won't experience an allergic reaction the first time you take a drug; you need to develop antibodies to it, just as you do with other types of allergies. Therefore, the longer or more frequently you take a drug, the greater the chance of developing an allergy.
  • How was the drug administered? Topical medications and injected medications are more likely to cause a reaction than those taken orally.
  • Your age. Adults are more likely to have an allergic reaction to medications than children.
  • Your dosage. The higher the dose, the more likely an allergic reaction.

If you are allergic to a drug, make sure to inform your physicians. The primary treatment is avoidance of the medication. A shot of epinephrine, a form of adrenaline, can be given to halt an anaphylactic reaction.

Since drug reactions are usually unanticipated, make sure you're within the reach of medical help when you first begin taking a medication. Don't go hiking alone in the mountains or sequester yourself away from human contact. Reactions typically occur within a few minutes to an hour, but they can occur much later. In fact, some can react days later or even after the antibiotic was stopped.

Yeast infections and loose stools are not symptoms of an allergic reaction.

While drug allergies are rare, the symptoms can be harmful. That's why it's important to locate and identify a drug allergy so that it may be properly treated.

©Publications International, Ltd.


This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

The brand name products mentioned in this publication are trademarks or service marks of their respective companies. The mention of any product in this publication does not constitute an endorsement by the respective proprietors of Publications International, Ltd. or, nor does it constitute an endorsement by any of these companies that their products should be used in the manner described in this publication.