The emphasis is on biological mechanisms underlying addiction, although some other factors influencing Drug Addiction Essay will also be discussed. The presentation is limited primarily to psychomotor stimulants (e.g., amphetamine, cocaine) and opiates (e.g.
, heroin, morphine) for two reasons. First, considerable knowledge has been gained during the past 15 years regarding the neurobiological mechanisms mediating their addictive properties. Second, these two pharmacological classes represent the best examples of potent addictive drugs, and the elucidation of their addiction potential can provide a framework for understanding abuse and addiction to other psychotropic agents.
Some psychologists and sociologists assert that animal studies do not model the important psychological variables governing drug addiction. They suggest that psychological processes critical in the etiology of addiction cannot be studied in animal models and/or that environmental influences important in producing an addiction cannot be duplicated in animal studies. This position is generally untenable, and animal models have been developed that accurately represent the primary processes involved in drug addiction.
Support for the validity of these animal models will emanate from an understanding of the characteristics and the neural basis of drug addiction summarized in the following sections.
The arguments presented in the chapter are tenable, but they represent only one of several perspectives used in studying addiction. The terminology and even some aspects of the empirical data are the topics of scientific debate. The objective of this chapter is not to provide a balanced presentation of controversial issues, but rather to develop a unifying framework for understanding the psychobiological basis of addiction.
Before proceeding with an examination of the mechanisms underlying drug addiction, it is necessary to define the term addiction and to examine the main characteristics of drug addiction. Delineation of the salient attributes of addiction helps to establish the criteria that must be fulfilled in a valid animal model and helps to determine what biological processes are relevant to the etiology of addiction.
Drug addiction refers to a situation where drug procurement and administration appear to govern the organism’s behavior, and where the drug seems to dominate the organism’s motivational hierarchy. Jaffe (1975) has described addiction as “a behavioral pattern of compulsive drug use, characterized by overwhelming involvement with the use of a drug, the securing of its supply, and a high tendency to relapse after withdrawal abstinence (p. 285).” This definition follows the general lexical usage of the term and is consistent with the word’s etymology (see Bozarth 1987a).
Drug addiction is defined behaviorally. It carries no connotations regarding the drug’s potential adverse effects, the social acceptability of drug usage, or the physiological consequences of chronic drug administration (Jaffe 1975).
This latter point is especially important because some investigators have mistakenly used the term addiction to describe the development of physical dependence (see Bozarth 1987a, 1989; Jaffe 1975). Although drug addiction frequently has adverse medical consequences, it is usually associated with strong social disapproval, and it is sometimes accompanied by the development of physical dependence, these factors do not define addiction nor are they invariably associated with it. Drug addiction is an extreme case of compulsive drug use associated with strong motivational effects of the drug.
Initial drug use can be motivated by a number of factors. Curiosity about the drug’s effects, peer pressure, or psychodynamic processes can all provide sufficient motivation for experimental or circumstantial drug use. If the drug is taken repeatedly, a period of casual drug use often develops.
Further use of the drug associated with more frequent drug administration, the use of higher drug dosages, and/or the use of more effective routes of administration (e.g., switching from intranasal to intravenous cocaine use) can lead to intensive patterns of drug use. Continued, more sustained drug use can then produce compulsive drug use where the substance has strong motivational properties and appears to govern much of the individual’s behavior. The most extreme case of drug use is the final progression to addiction.
Drug use is viewed as a continuum, progressing from casual use to addiction (see Jaffe 1975); the drug assumes increasing control of the individual’s behavior as the pattern of drug use approaches addiction.
Jaffe (1975) suggests that addiction is an extreme case of drug use that is not qualitatively different, but .