Medication/Drug Allergy Make an Appointment Find a Doctor Ask a Question Reviewed by Christine B. Cho, MD (December 01, 2016) Reactions to medications/drugs can cause a wide variety of signs and symptoms that may affect various organs or parts of the body. Medications can cause adverse side effects that are often confused with allergic reactions. The difference between an adverse effect and allergic reaction is that true medication allergy is caused by an immune reaction to the medication. Allergic reactions can be potentially life-threatening. One characteristic of all medication allergies is that similar symptoms will occur every time after the offending medication is taken. Penicillin and other antibiotics are the medication that most commonly cause allergic reactions. Women appear to have an increased risk for adverse reactions to medications. Facts about Allergies The tendency to develop allergies may be inherited. If you have allergic tendencies and are exposed to certain things in your environment (allergens), you may develop allergies to some of those things. Common examples of allergens include animal dander, dust mites, pollens and molds. Examples of allergy symptoms and allergic conditions include itchy eyes, runny nose, asthma, eczema (atopic dermatitis) and hives (urticaria). The timing of the allergic response may be immediate or delayed. What Is an Allergy to Medication/Drugs? Allergies to drugs/medications are complicated, because they can be caused by many different medications, resulting in a wide variety of signs and symptoms that may affect various organs or parts of the body. Furthermore, some drugs can cause adverse effects whose symptoms closely resemble those of an allergic reaction. The difference is that true drug allergy is caused by a hypersensitive immune system that creates IgE and other antibodies and/or cytotoxic immune cells in response to an otherwise harmless substance in the medication. One characteristic of all drug allergies is that similar symptoms will occur every time soon after the offending medicine is taken. Programs & Services Allergy Treatment Programs (Adult) Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.