context: Many medications can cause adverse side effects and certain drugs can trigger allergic reactions. In the case of allergic reactions, when a drug first enters the body, the immune system mistakenly responds by creating specific disease-fighting antibodies, called immunoglobulin E, or Ig E antibodies. These antibodies recognize the drug as a foreign substance. When the drug is taken again, these antibodies spring into action, releasing large amounts of histamine in an attempt to expel the drug from the body. Histamine is a powerful chemical that can affect the respiratory system, gastrointestinal tract, skin, or cardiovascular system. Symptoms of a drug allergy can range from mild to life-threatening. Even in people who aren't allergic, many drugs can cause irritation, such as an upset stomach. But during an allergic reaction, the release of histamine can cause signs like hives, skin rash, itchy skin or eyes, and congestion. A more severe reaction may include swelling in the mouth and throat, difficulty breathing, blueness of the skin, dizziness, fainting, anxiety, confusion, rapid pulse, nausea, diarrhea, and abdominal problems. The most common drug associated with allergies is penicillin. Other antibiotics similar to penicillin can also trigger allergic reactions. Other drugs commonly found to cause reactions include sulfa drugs, barbiturates, anticonvulsants, tetracycline, aspirin, and iodine (found in many X-ray contrast dyes). A doctor diagnoses a drug allergy by carefully reviewing your medical history and symptoms. If your doctor suspects that you are allergic to an antibiotic such as penicillin, he or she may do a lab or skin test to confirm it. However, skin testing does not work for all drugs, and in some cases it can be dangerous. In rare cases, it may be necessary to test for a drug allergy by actually giving small doses of the suspected medicine. But this may trigger a life threatening anaphylactic reaction, so it should only be done under certain circumstances at special allergy centers. If you have had a severe, life-threatening reaction to a particular drug, your doctor may simply rule out that drug as a treatment option for you. Conducting an allergy test to determine if the initial reaction was a "true" allergic response may not be worth the risk. The primary goal when treating drug allergies is symptom relief. Symptoms such as rash, hives, and itching can often be controlled with antihistamines and occasionally corticosteroids. For coughing and lung congestion, drugs called bronchodilators may be prescribed to widen the airways. For more serious anaphylactic symptoms -- life-threatening reactions including difficulty breathing or loss of consciousness -- epinephrine may be needed. Call 911 for any of these symptoms. Occasionally, desensitization is used for penicillin allergy. This technique decreases your body's sensitivity to particular allergy-causing agents. Tiny amounts of penicillin are injected periodically in increasingly larger amounts until your immune system learns to tolerate the drug. If you are severely allergic to certain antibiotics, there are usually alternative antibiotics your doctor can prescribe when needed. If you have a drug allergy, you should always inform your health care provider before undergoing any type of treatment, including dental care. It is also a good idea to wear a Medic Alert bracelet or pendant, or carry a card that identifies your drug allergy. In cases of emergency, it could save your life.