DefinitionDrug Allergies are a group of symptoms caused by an allergic reaction to a drug (medication).Alternative NamesAllergic reaction - drug (medication); Drug hypersensitivity; Medication hypersensitivityCauses, incidence, and risk factorsAdverse reactions to drugs are common, and almost any drug can cause an adverse reaction. Reactions range from irritating or mild side effects such as nausea and vomiting to life-threatening anaphylaxis.A true drug allergy results from a series of chemical steps within the body that produce the allergic reaction to a medication.It can develop two different ways:The first time you take the medicine, you have no problems, but your body's immune system produces a substance (antibody) called IgE against that drug. The next time you take the drug, the IgE