Definition of Side Effect
Side Effect is an action other than the intended therapeutic effect of a drug – may be neutral, beneficial, or harmful.
Many side effects are so common as to be expected, such as diarrhea with certain antibiotic medications (which occurs because antibiotics kill bacteria, including the bacteria that normally reside in the gastrointestinal tract to aid in digestion).
Some side effects are temporary, such as drowsiness when first beginning treatment with antidepressant medications (which affect neurotransmitters and functions of the central nervous system) and nausea at the onset of therapy with antihypertensive medications (which affect the autonomic nervous system).
A harmful side effect (one that has serious or long-term health consequences) is an adverse drug reaction. It is important to know what side effects can occur with all medications a person is taking, for each individual drug as well as for the drugs in combination with each other.
In the United States federal and state laws require product package inserts or label information to contain brief information about possible side effects.
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