A drug is defined by U.S. law as any substance (other than a food
or device) intended for use in the diagnosis, cure, relief, treatment,
or prevention of disease or intended to affect the structure or function
of the body. (Oral contraceptives are an example of drugs that affect
the function of the body rather than a disease.) This comprehensive
definition of a drug, although important for legal purposes, is rather
complex for everyday use. A simpler but workable definition of a drug is
any chemical or biologic substance that affects the body and its
processes.
Some people incorrectly use the word drug to mean only a
substance that produces a pleasurable sensation. The excessive and
persistent use of mind-altering substances without medical need has
accompanied the appropriate medical use of drugs throughout recorded
history. Some of the drugs that fall into this category have legitimate
medical purposes, and others do not (see Overview of Substance-Related Disorders).
Prescription drugs or nonprescription drugs
By law, drugs are divided into two categories: prescription drugs and nonprescription drugs.
Prescription drugs—those considered safe for use only
under medical supervision—may be dispensed only with a prescription from
a licensed professional with governmental privileges to prescribe (for
example, a doctor, dentist, podiatrist, nurse practitioner, physician's
assistant, or veterinarian).
Nonprescription drugs—those considered safe for use without medical supervision (such as aspirin)—are sold over the counter.
In the United States, the Food and Drug Administration (FDA) is the
government agency that decides which drugs require a prescription and
which may be sold over the counter.
Dietary supplements
(for example, medicinal herbs and nutraceuticals) are products intended
to supplement the diet. These products may contain vitamins, amino
acids, minerals, and herbs or other plant-derived material (botanicals).
Because dietary supplements are not classified as drugs, they do not
require FDA approval before marketing and do not have to meet the same
standards as drugs for safety and efficacy.
Although these products are not classified as drugs, they can act in
the same way as a drug does in the body and may cause health problems if
not used correctly or if taken in large amounts. Because these products
do not meet the FDA standards for safety and efficacy, they may not
claim to treat specific medical conditions.
Drug names
Some knowledge of drug names can help in understanding drug
product labels. Every drug has at least three names—a chemical name, a
generic (nonproprietary or official) name, and a brand (proprietary or
trademark) name (see sidebar What's In a Name?).
The chemical name describes the atomic or molecular
structure of the drug. This name is usually too complex and cumbersome
for general use. So an official body assigns a generic name to a drug.
The generic names for drugs of a particular type (class)
usually have the same ending. For example, the names of all
beta-blockers, which are used to treat such disorders as high blood
pressure, end in "lol" (such as metoprolol and propranolol).
The brand name is chosen by the pharmaceutical company
that manufactures or distributes the drug. Patented drugs are usually
sold under a brand name. Generic versions of brand-name
drugs—manufactured after expiration of the pharmaceutical company's
patent—may be sold under the generic name (for example, ibuprofen) or under the manufacturer's own brand name (for example, Advil).
Drug groups
Understanding what group a drug belongs to is also useful.
Broadly, drugs are classified by therapeutic group—that is, by what
disorder or symptom they are used to treat. For example, drugs used to
treat high blood pressure are called antihypertensives (hypertension is
the medical term for high blood pressure), and drugs used to treat
nausea are called antiemetics (emesis is the medical term for vomiting).
Within each therapeutic group, drugs are categorized by classes. Some
classes are based on how the drugs work in the body to produce their
effect. For example, diuretics, calcium channel blockers, beta-blockers,
and angiotensin-converting enzyme (ACE) inhibitors are all classes of
antihypertensives that work differently.
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