A

adverse drug reaction An undesired, negative,
and often unpleasant response to a medication.
People commonly refer to adverse DRUGreactions
as side effects, which is not entirely accurate
because a SIDE EFFECTmay have therapeutic value
whereas an adverse drug reaction is potentially
harmful. Adverse drug reactions are common,
affecting more than two million Americans each
year. They can occur with any drug a person takes
or uses, ranging in severity from upset STOMACHor
HEADACHE, which often subside after taking the
drug for several doses, to URTICARIA(hives) or ANA-
PHYLAXIS(life-threatening closure of the airways),
which are usually allergic reactions. RASH and
itching are also common adverse reactions.
Adverse drug reactions may also affect the compo-
sition of the BLOODor the function of organs such
as the HEART, LIVER, andKIDNEYS.

Intentional misuse of a DRUG, including

taking more than recommended or in

combination with other drugs, increases

the likelihood of adverse drug reaction.

All drugs have some identified potential
adverse reactions. These are the events that usu-
ally surface during the human testing phase of
clinical research studies. Some such reactions may
be inherent to the properties of the drug—that is,
result from the drug itself. Many ANTIBIOTIC MED-
ICATIONS, for example, kill BACTERIAin the intes-
tines at the same time they kill bacteria that are
causing INFECTION, resulting in DIARRHEAbecause
intestinal bacteria are essential for proper diges-
tion. NAUSEA, VOMITING, and HAIRloss are known
adverse reactions with CHEMOTHERAPYdrugs. Other
such reactions may result from DRUG INTERACTIONS
with other medications the person is using or from

the ways in which the body responds to the drug

over the long term. Tardive DYSKINESIAis a known

adverse reaction to long-term use of ANTIPSYCHOTIC

MEDICATIONS, for example. Long-term use of CORTI-

COSTEROID MEDICATIONS, such as taken to treat

INFLAMMATORY BOWEL DISEASE(IBD) or ADDISON’S DIS-

EASE, have numerous adverse effects on the body.

Adverse drug reactions may be localized, such

as DERMATITIS, or systemic (involve multiple body

systems). Doctors generally classify adverse drug

reactions as immunologic (those that involve an

IMMUNE RESPONSE) or nonimmunologic (those that

do not involve an immune response). People who

are IMMUNOCOMPROMISED(such as those who have

HIV/AIDSor take IMMUNOSUPPRESSIVE THERAPY), have

an autoimmune disorder such as RHEUMATOID

ARTHRITIS or SYSTEMIC LUPUS ERYTHEMATOSUS (SLE),

have liver or kidney disease, take multiple med-

ications (often called polypharmacy), or are age 60

or older have increased risk for adverse drug reac-

tions. Most drug reactions occur within several

days to three weeks of beginning the drug, though

some long-term adverse reactions occur up to

years after the drug’s initiation.

COMMON ADVERSE DRUG REACTIONS

allergic response ANAPHYLAXIS ANEMIA

ANGIOEDEMA ARRHYTHMIA arthralgia

CANDIDIASIS DERMATITIS DIARRHEA

GLOMERULONEPHRITIS LYMPHADENOPATHY NEUTROPENIA

PRURITUS RASHon trunk tardive DYSKINESIA

TINNITUS URTICARIA VOMITING

It is important, when beginning treatment with

a new medication or adding a different drug to a

treatment regimen, to know the expected results

and possible adverse reactions. People who take

multiple drugs, including OVER-THE-COUNTER(OTC)

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