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A drug allergy is "an unintended immune response to the medication". Some people get a mild rash, others experience shortness of breath, and some even die. Drug allergies are actually much less common than drug side effects.

An allergic reaction occurs when the immune system reacts to the presence of a foreign substance. The body is trying get rid of the substance. In a drug allergy this response is harmful, and can sometimes cause serious symptoms.

"Side effects" are unpleasant things that happen as a result of taking a drug. Side effects that are common to medicines include drowsiness, dry mouth, nausea, diarrhea, vomiting, headache, and lightheadedness. These side effects often go away after a period of time, even if the person continues taking the drug.

Symptoms of a drug allergy may include:

• anaphylactic shock, a very severe reaction that can lead to death
• anxiety
• hives, which are multiple small, itchy, swollen areas on the skin
• palpitations, which are an unusual awareness of the heart beating within the chest
• shortness of breath
• skin rash
• swelling of one or more parts of the body
• wheezing