Drug reactions

Drug allergies are a group of symptoms caused by an allergic reaction to a drug (medicine).

Causes

A drug allergy involves an immune response in the body that produces an allergic reaction to a medicine.

The first time you take the medicine, you may have no problems. But, your body’s immune system may produce a substance (antibody) against that drug. The next time you take the drug, the antibody may tell your white blood cells to make a chemical called histamine. Histamines and other chemicals cause your allergy symptoms. The reaction of the body when a drug allergy is present generally involves special cells called B and T cell lymphocytes.