See alsoILLICIT 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 gastroin-
testinal tract to aid in digestion). Some side effects
are temporary, such as drowsiness when first
beginning treatment withANTIDEPRESSANT MEDICA-
TIONS(which affect neurotransmitters and func-
tions of the CENTRAL NERVOUS SYSTEM) and NAUSEAat
the onset of therapy with antihypertensive med-
ications (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 prod-
uct 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.side effect 171