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As generally understood, drug abuse includes any illicit use of a drug for nonmedical purposes, usually for altering consciousness, but also for body building. The term also denotes the deliberate use of chemicals that are generally not considered drugs by the lay public, but may be harmful to the user. Often, the motivation for drug abuse appears to be the anticipated feeling of pleasure derived from the central nervous system (CNS) effects of the drug. If physiologic dependence is present, preventing a withdrawal or abstinence syndrome reinforces continued drug abuse.


The term drug abuse connotes social disapproval and may have different meanings to different people. One may also distinguish drug abuse from drug misuse. To misuse a drug might be to take it for the wrong indication, in the wrong dosage, or for too long a period. In the context of drug abuse, the drug itself is of less importance than the pattern of use. For example, taking 50 mg of diazepam to heighten the effect of a daily dose of methadone is an abuse of diazepam. On the other hand, taking the same excessive daily dose of the drug, but only for its anxiolytic effect, is misusing diazepam.


In this chapter, we discuss the terminology relevant to drugs of abuse, the socioeconomic and cultural considerations of such drug use, and the major classes of these drugs along with some examples from each class. The major classes of drugs that are abused are presented in Figure 21–1, and prototypic agents of each class are presented in Table 21–1.

Figure 21–1.
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Major classes of drugs of abuse. LSD = lysergic acid diethylamide; PCP = phencyclidine.

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Table 21–1. Major Classes of Drugs of Abuse with Prototypic Substances and Additional Abused Substances 

Dependence refers to the biologic phenomena often associated with drug abuse. Psychologic dependence is manifested by compulsive drug-seeking behavior in which the individual uses the drug repetitively for personal satisfaction, often despite known risks to health. Deprivation of the agent for a short period of time typically results in a strong desire or craving for it. Cigarette smoking is one example. Physiologic dependence is present when withdrawal of the drug produces ...

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