Question: Are allergic reactions to medicine the same as side effects?
A: When someone has an unexpected reaction to a medication they have taken, it is usually because one of two things is happening inside their body. They are either experiencing a side effect of the drug, or they are having an allergic reaction to it.
Drug side effects are usually not serious, almost always a byproduct of the intended therapeutic effect of the drug that was taken and are more common than allergic reactions. For instance, drugs developed to lower blood pressure can produce the side effect of dizziness. People who take medications for their high blood pressure may become dizzy when they stand because their lowered blood pressure may not be sufficient to rapidly deliver enough blood to the brain when standing from a seated position.
Allergic reactions to a drug are completely different from side effects. They are an immune response by the body in reaction to the medication being introduced into the system. When this occurs, the body believes the drug to be harmful, so antibodies release histamine into the bloodstream, which works to try to eliminate the drug. This reaction is not desirable and is potentially harmful and life-threatening.
Someone experiencing an allergic reaction to a prescribed medication typically develops hives, a rash, itchiness, congestion or swelling in the throat. Antihistamines like Benadryl can help to provide relief from symptoms in mild reactions. Severe reactions may result in anaphylaxis – a state of widespread bodily dysfunction often causing vomiting/diarrhea, difficulty breathing, dizziness, seizures, weak/irregular pulse, low blood pressure or loss of consciousness. If this occurs, administer epinephrine (EpiPen) if available and seek immediate emergency medical attention.
Regardless of their severity, people need to become familiar with any drug allergies they may have and share the information with their physicians so they can avoid prescribing problematic medications. A board-certified allergist will be able to take a careful history and perform the testing necessary, if available, to tell you which drugs are safe to take. For those with drug allergies, medic alert devices, such as bracelets, should be worn with the drug allergy noted in case of an emergency.
– Marc W. Cromie, M.D., allergy and asthma specialist with Chattanooga Allergy Clinic; Chattanooga-Hamilton County Medical Society member