Definition:
An adverse reaction is an unwanted or unexpected negative reaction to a medication or treatment that is used in an approved manner.
Adverse reactions can be mild, such as a simple rash, or severe and life-threatening in nature. They can occur immediately when a treatment is started, or develop over time. Some adverse reactions are common, and can be anticipated by your doctor, whereas others occur very rarely.
If you suspect you are having an adverse reaction to a medication or treatment, it is important to let your doctor know as soon as possible.
Examples:
Evelyn developed hives when she began the new medication to help with her lung cancer. Her oncologist told her this was an adverse reaction that some people have, and recommended a different medication.
