In order for a chemical to be considered a drug it must have the capacity to affect how
the body works--to be biologically active. No substance that has the power to do this is
completely safe, and drugs are approved only after they demonstrate that they are
relatively safe when used as directed, and when the benefits outweigh their risks. Thus,
some very dangerous drugs are approved because they are necessary to treat serious
illness. Digitalis, which causes the heart muscle to contract, is a dangerous drug, but
doctors are permitted to use it because it is vital for treating patients whose heart
muscle is weak. A drug as potent as digitalis would not be approved to treat such minor
ailments as temporary fatigue because the risks outweigh the benefits.
Many persons suffer ill effects from drugs even though they take the drug exactly as
directed by the doctor or the label. The human population, unlike a colony of ants or
bees, contains a great variety of genetic variation. Drugs are tested on at most a few
thousand people. When that same drug is taken by millions, some people may not respond in
a predictable way to the drug. A person who has a so-called idiosyncratic response to a
particular sedative, for example, may become excited rather than relaxed. Others may be
hypersensitive, or extremely sensitive, to certain drugs, suffering reactions that
resemble allergies.
A patient may also acquire a tolerance for a certain drug. This means that ever-larger
doses are necessary to produce the desired therapeutic effect. Tolerance may lead to
habituation, in which the person becomes so dependent upon the drug that he or she
becomes addicted to it. Addiction causes severe psychological and physical disturbances
when the drug is taken away. Morphine, cocaine, and Benzedrine are common habit-forming
drugs. Finally, drugs often have unwanted side effects. These usually cause only minor
discomfort such as a skin rash, headache, or drowsiness. Certain drugs, however, can
produce serious, even life-threatening adverse reactions. For example, the drug
Thalidomide was once called one of the safest sedatives ever developed, but thousands of
women in the United Kingdom who took it during pregnancy gave birth to seriously deformed
babies. Other adverse reactions stem from mixing drugs. Thus, taking aspirin, which has
blood-thinning qualities, for a headache can be very harmful if one is also taking other
blood-thinning drugs such as heparin or dicumarol.
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