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Drug abuse is usually taken to mean the use of an illicit drug or the excessive or nonmedical use of a licit drug. It also denotes the deliberate use of chemicals that generally are not considered drugs by the lay public but may be harmful to the user. A primary motivation for drug abuse appears to be the anticipated feeling of pleasure derived from the CNS effects of the drug. The older term "physical (physiologic) dependence" is now generally denoted as dependence, whereas "psychological dependence" is more simply called addiction.

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Abstinence syndromeA term used to describe the signs and symptoms that occur on withdrawal of a drug in a dependent person
AddictionCompulsive drug-using behavior in which the person uses the drug for personal satisfaction, often in the face of known risks to health; formerly termed psychological dependence
Controlled substanceA drug deemed to have abuse liability that is listed on governmental Schedules of Controlled Substances.a Such schedules categorize illicit drugs, control prescribing practices, and mandate penalties for illegal possession, manufacture, and sale of listed drugs. Controlled substance schedules are presumed to reflect current attitudes toward substance abuse; therefore, which drugs are regulated depends on a social judgment
DependenceA state characterized by signs and symptoms, frequently the opposite of those caused by a drug, when it is withdrawn from chronic use or when the dose is abruptly lowered; formerly termed physical or physiologic dependence
Designer drugA synthetic derivative of a drug, with slightly modified structure but no major change in pharmacodynamic action. Circumvention of the Schedules of Controlled Drugs is a motivation for the illicit synthesis of designer drugs
ToleranceA decreased response to a drug, necessitating larger doses to achieve the same effect. This can result from increased disposition of the drug (metabolic tolerance), an ability to compensate for the effects of a drug (behavioral tolerance), or changes in receptor or effector systems involved in drug actions (functional tolerance)

aAn example of such a schedule promulgated by the US Drug Enforcement Agency is shown in Table 32–1. Note that the criteria given by the agency do not always reflect the actual pharmacologic properties of the drugs.

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Dopamine in the mesolimbic system appears to play a primary role in the expression of "reward," but excessive dopaminergic stimulation may lead to pathologic reinforcement such that behavior may become compulsive and no longer under control—common features of addiction. Though not necessarily the only neurochemical characteristic of drugs of abuse, it appears that most addictive drugs have actions that include facilitation of the effects of dopamine in the CNS.

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The sedative-hypnotic drugs are responsible for many cases of drug abuse. The group includes ethanol, barbiturates, and benzodiazepines. Benzodiazepines are commonly prescribed drugs for anxiety and, as Schedule IV drugs, are judged by the US government to have low abuse liability (Table 32–1). ...

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