Abnormal drowsiness may be the result
of a head injury, high fever, meningitis,
uraemia(excess urea in the blood due to
kidney failure), or liver failure. Alcohol or
drugs may also produce this effect. In a
person with diabetes mellitus, drowsiness
may be due to hypoglycaemiaor to hyper-
glycaemia. Abnormal drowsiness should
be treated as a medical emergency.
drugA chemical substance that alters
the function of one or more body organs
or the process of a disease. Drugs
include prescribed medicines, over-the-
counter remedies, and substances
(such as alcohol, tobacco, and drugs of
abuse) that are used for nonmedical
purposes. Drugs normally have a chem-
ical name, an officially approved generic
name (seegeneric drug), and often a
brand name. Drugs for medical use are
either licensedfor prescription by a doc-
tor only or can be bought over the
counter at a chemist’s or supermarket.
Most drugs are artificially produced to
ensure a pure preparation with a pre-
dictable potency (strength). Some drugs
are genetically engineered. A drug is
classified according to its chemical
make-up or the disorder it treats or,
according to its specific effect on the
body. All new drugs are tested for their
efficiency and safety. In the UK, drugs
are licensed by the Medicines Control
Agency (MCA). A licence may be with-
drawn if toxic effects are reported or if
the drugs causes serious illness.
Drugs can be used to relieve physical
or mental symptoms, to replace a de-
ficient natural substance, or to stop the
excessive production of a hormoneor
other body chemical. Some drugs are
given to destroy foreign organisms,
such as bacteria. Others, known as vac-
cines, are given to stimulate the body’s
immune systemto form antibodies.
Drugs are given by mouth, by injection,
or applied directly to the affected site
via transdermal, nasal, and other direct
routes (for example, to the lungs through
an inhaler). Injected drugs have a more
rapid effect than drugs taken by mouth
because they enter the bloodstream
without passing first through the diges-
tive system. Unabsorbed drugs taken by
mouth are excreted in the faeces. Drugs
that have entered the bloodstream are
eliminated in urine. Some drugs interact
with food or alcohol or other drugs. Most
drugs can produce adverse effects. These
effects may wear off as the body adapts
to the drug. Adverse effects are more
likely if there is a change in the absorp-
tion, breakdown, or elimination of a
drug (caused, for example, by liver dis-
ease). Unexpected reactions sometimes
occur due to a genetic disorder, an
allergic reaction, or the formation of
antibodies that damage tissue.
Many drugs cross the placenta; some
affect growth and development of the
fetus. Most drugs pass into the breast
milk of a nursing mother, and some will
have adverse effects on the baby.
drug abuseUse of a drug for a purpose
other than that for which it is normally
prescribed or recommended. Commonly
abused drugs include stimulant drugs,
such as cocaineand amfetamine drugs;
central nervous system depressants,
such as alcoholand barbiturate drugs;
hallucinogenic drugs, such as LSD; and
narcotics (see opioid drugs), such as
heroin. Some drugs are abused in order
to improve performance in sports (see
sports, drugs and; steroids, anabolic).
Problems resulting from drug abuse
may arise from the adverse effects of
the drug, accidents that occur during
intoxication, or from the habit-forming
potential of many drugs, which may
lead to drug dependence.
drug addictionPhysical or psycho-
logical dependence on a drug (see
drug dependence).
drug dependenceThe compulsion to
continue taking a drug, either to pro-
duce the desired effects of taking it, or
to prevent the ill-effects that occur when
it is not taken. Drug dependence can be
psychological or physical. A person is
psychologically dependent if he or she
experiences craving or emotional dis-
tress when the drug is withdrawn. In
physical dependence, the body has
adapted to the drug, causing the symp-
toms and signs of withdrawal syndrome
when the drug is stopped. Symptoms
are relieved if the drug is taken again.
Drug dependence develops as a result
of regular or excessive drug use, and itDRUG DRUG DEPENDENCE
D