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Drug Allergies

Adverse reactions to medications are common, yet everyone responds differently. One person may develop a rash or other reactions when taking a certain type of medication, while another person on the same drug may have no adverse reaction at all.

Only about 5% to 10% of these reactions are due to an actual allergy to the medication.

An allergic reaction occurs when the immune system overreacts to a harmless substance, in this case a medication, which triggers an allergic reaction. “Sensitivities” to drugs may produce similar symptoms, but this type of reaction would not involve the immune system.

Certain medications are more likely to produce allergic reactions than others. Some common examples are:

  • Antibiotics (such as penicillin)
  • Aspirin and non-steroidal anti-inflammatory medications such as ibuprofen
  • Anticonvulsants
  • Monoclonal antibody therapy
  • Chemotherapy


Reactions to medications range from vomiting and hair loss with cancer chemotherapy to upset stomach from aspirin or diarrhea from antibiotics. If you take ACE (angiotensin converting enzyme) inhibitors for high blood pressure, you may develop a cough or facial and tongue swelling.

In many cases, it can be difficult to determine if the reaction is due to the medication or something else. This is because your symptoms may be similar to other conditions.

The most frequent types of allergic symptoms to medications are:

  • Skin rashes, particularly hives
  • Itching
  • Respiratory problems
  • Swelling, such as in the face
  • Anaphylaxis (Anaphylaxis is a serious allergic response that often involves more than one system of the body like swelling, hives, lowered blood pressure or in severe cases, shock. Anaphylactic shock is a severe condition and if it isn’t treated immediately, it can be fatal.)