Encyclopedia of Health and Medicine

side effect 171
See also ILLICIT DRUG USE; LEGEND DRUG; OVER-THE-
COUNTER (OTC) DRUGS; PRESCRIPTION DRUG ABUSE.
side effect An action other than the intended
therapeutic effect of a DRUG. Side effects may be
neutral, beneficial, or harmful. Many side effects
are so common as to be expected, such as DIAR-
RHEA 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 MEDICA-
TIONS (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 SYS-
TEM). 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.
See also ALCOHOL INTERACTIONS WITH MEDICATIONS;
DRUG INTERACTION; NEUROTRANSMITTER; OFF-LABEL USE.