Introduction
A drug is defined by United States 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 substance that affects the body and its processes.
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 physician, 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 (see Section 2, Chapter 18). 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. (Alternative medicines, such as nutraceuticals and medicinal herbs (see Section 2, Chapter 19), are not covered by this law; they have not undergone the stringent testing required by the FDA.)
To some people, the word drug means a substance that alters the brain's function in ways considered pleasurable--a mind-altering substance. Drug abuse--the excessive and persistent use of mind-altering substances without medical need--has accompanied the appropriate medical use of drugs throughout recorded history. Some drugs with potential for abuse have legitimate medical purposes, and others do not (see Section 7, Chapter 108).
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 trade (proprietary or brand) 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 usually, 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 "olol."
The trade name is chosen by the pharmaceutical company that manufactures or distributes the drug. Patented drugs are usually sold under a trade name. Generic versions of trade-name drugs--manufactured after expiration of the patent--may be sold under the generic name (for example, ibuprofen) or under their own trade name (for example, Advil).
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, and drugs used to treat nausea are called antiemetic drugs (emesis is the technical 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, calcium channel blockers, one class of antihypertensives, lower blood pressure by preventing calcium from entering certain cells. Calcium is necessary for the contraction of muscles, including those in the walls of arteries. So calcium channel blockers hinder the contraction of muscles in artery walls and thus cause arteries to widen, so that blood can flow through them more easily. Calcium channel blockers affect the contraction of heart muscle less, and they do not interfere with the contraction of muscles under conscious control (skeletal muscle).
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