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There are several criteria in terms of which it is meaningful to evaluate a drug involvement for its addictive potential. Some of these criteria derive from initial motivations for using a drug and from the motivations for continuing use. If a drug is used in order to eradicate consciousness of pain, problems, and anxieties, then its use will tend to be addictivě. Another aspect of this type of abuse is the inability of users to derive pleasure from drug use, since they are relying on the drug primarily to avoid unpleasantness rather than for any positive effect. In this case, a criterion for abuse and addiction is that the drug is relied on at regular times for the very predictability of its effects. The most crucial criterion for the addictiveness of an involvement is whether use of the drug destroys or harms other involvements. For when this is the case, abuse moves inexorably along the continuum toward addiction as other reinforcers fall away, and the drug experience becomes the primary source of reward for the individual.

The sign of addiction is the absence of a degree of choice about drug use. The sense of suitability or appropriateness, where certain situations or people rule out use of the drug, is lost. Also lost is the capability for making discriminations with regard to the experience the drug produces. That is, addicts will not reject a brand of cigarette, a type of alcohol, or a narcotic of inferior purity, since they are interested in only the grossest sensations of the drug experience. Finally, identity and continued functioning have become so connected to the effects of the drug that it is impossible for the addict to conceive of life proceeding without the drug.

(p. 286)

SOCIAL NEUROBIOLOGICAL THEORY
Prescott

The transition from use to abuse of psychochemical substances according to somatosensory affectional deprivation (SAD) theory is dependent upon the following factors:

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2. Duration of SAD. 3. Severity of SAD. 4. Nature, quality, duration, and time period during formative periods

of development of intervening, restorative, and rehabilitative experiences of somatosensory affectional relationships. Absence of such experiences is considered to be particularly pathogenic for abusive behaviors.

5.

Nature, quality , duration, and time period during formative periods of development of other experiences or factors that result in impaired somesthetic and vestibular functioning, which intereferes with the rehabilitation of somatosensory affectional processes. In general, it is the chronic failure, for whatever reasons, to experience the enrichment of somatosensory affectional experiences in the context of meaningful relationships that sets the condition for the transition from use to abuse. Individuals who do not or cannot make the transition from states of "reflexive" pleasure to states of

"integrative" pleasure are at risk for making the transition from
substance use to substance abuse (Prescott 1977).

(p. 215)

NATURAL HISTORY PERSPECTIVE
Robins

Typical patterns of changes in dosage of illicit drugs over time have been difficult to study because the strength of street drugs varies so greatly over time and from one location to another that changes in frequency of administration cannot be readily interpreted as changes in dosage. In addition, fluctuating availability and cost greatly influence use patterns. It does appear, however, that frequency of use tends to increase over time, suggesting the development of tolerance to most illicit drugs. How much tolerance develops can be studied only in experimental settings where amount of access to drugs of standard quality is known. Such experiments have been carried out in prisons where prisoners were allowed free access to marijuana cigarettes of standard quality. They were found to use up to 17 or 18 a day. Thus there may be a maximum amount of cannabis that can be metabolized in a day, just as there is for alcohol.

It is known that illicit drugs vary greatly in their addictive potential. It was inferred from laboratory experiments showing the high addiction liability of heroin that first use of heroin would progress rapidly to regular use and then to daily use. This assumption seemed to be confirmed by observing the high rate of relapse to addiction of treated addicts, about two-thirds of whom generally appear to be readdicted within six months after treatment (Stephens and Cottrell 1972). Recent research, however, shows that heroin as used in the streets of the United States does not differ from other drugs in its liability to being used regularly or on a daily basis. O'Donnell et al. (1976) compared the frequency of progression to regular use among men who had ever used a particular drug. He defined regular use as at least twice a month. Progression to regular use was most common for alcohol. All but nine percent of drinkers drank at least as frequently as twice a month. Stimulants and heroin had similar rates--about half of the users ever became regular users. Marijuana showed the least progression to regular use, with only one-third of users doing so. Among users, likelihood of daily use was similar for heroin and for alcohol; that is, about one-third of those who ever used either drug began to use it on a daily basis. Marijuana was next most commonly used on a daily basis, with one-quarter progressing to that level, while only one in ten stimulant users ever became daily users.

Our study of Vietnam veterans found this same pattern for heroin use in the United States. While most narcotic users in Vietnam had progressed to regular use, and half became addicted, in the States heroin was not distinctive from other drugs in the likelihood that men would progress to regular or daily use of it. It may well be that the high addiction liability of heroin found in laboratory experiments and in Vietnam does not apply to the very adulterated product typically purchased in the streets.

What was distinctive about heroin among the returned veterans was that daily users were much more likely to perceive themselves as dependent on the drug than were daily users of barbiturates, amphetamines, or marijuana.

A common belief that has turned out to be largely a myth is that once heroin use begins, it tends to continue indefinitely. O'Donnell et al. (1976) found that of all men aged 20 to 30 who had ever used heroin, only 31 percent had taken any of the drug within the last year. Their rate of continuation with heroin was lower than the continuation rate for any other drug. Those who had ever used stimulants, sedatives, or cocaine had used some of that drug in the last year in about one-half of cases. Those who had ever used marijuana had used some in the last year in two-thirds of cases. Those who had used tobacco or alcohol had almost all used some within the last year. Thus there seems to be much more movement out of heroin use than there is out of use of other drugs. There is remarkably little movement out of the use of tobacco, despite health warnings by the Government.

Again, the same findings applied to the Vietnam veterans. Nearly half of them used narcotics at least once while in Vietnam, and more than one-fourth had used them at least weekly there for a month or more. Nonetheless, at the time we studied them when they had been back in the States three years, they were hardly more likely to be using narcotics than were nonveterans. Thus we found no special likelihood for the use of heroin to persist even among those who had used it regularly. In their second and third postwar years, veterans were no more often readdicted than were nonveterans. (Only two percent of either group were addicted at any time during this period.) The readdiction rate of Vietnam addicts was only 12 percent within the three post-Vietnam years. Our results and those of O'Donnell show that, given the heroin market of the 1970s in the United States, it is possible to use heroin occasionally without becoming addicted. It is still not known how long such occasional use can persist. The time over which addicts have used heroin prior to becoming addicted varies enormously, according to Waldorf (1973). The addicts he studied reported use anywhere from three weeks to six years prior to their first experience of addiction.

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The greatest impact of genetics might hypothetically occur in the transition between use and abuse. The best data on this subject are available for alcohol.

In a heavy-drinking society such as ours, strong social factors probably predominate in determining whether an individual will begin drinking and in the decision to take the substance two, three, or more times. The genetically influenced biological factors might have their greatest impact in explaining why in the mid-twenties to thirties most individuals decrease their drinking, while some maintain their high level of intake and even increase their consumption.

in the genetic theoretical framework, each individual enters life with a variety of genetically influenced factors which interact to give a level of biological predisposition toward alcoholism. The best guess, based on family and twin studies, would be either that multiple genes are involved (i.e., a polygenic inheritance) or that one major gene exerts

its effect differently in different circumstances (i.e., incomplete penetrance). This genetic predisposition would help to explain why some individuals go on to alcoholism after a number of years of limited drinking while others cut down their intake over time.

The factors could be any one or a combination of such things as a differential metabolism of alcohol, a biologically mediated differential sensitivity to the acute affects of alcohol, differences in subacute affects (e.g., acute tolerance), a differential sensitivity to organ-system damage in the presence of chronic exposure to alcohol, different predisposing personalities, etc. In each of these areas, the genetically influenced biological factors could help either to protect some people from becoming alcoholic (e.g., having an adverse acute reaction to alcohol, such as strong facial flushing (Seto et al. 1978]) or to predispose the person toward alcoholism (e.g., having an acute reaction to alcohol which is less intense than that of other individuals, thus leading to intake of higher levels of ethanol to obtain the same pleasant effects as nonpredisposed individuals).

The persons thus predisposed would enter their early drinking years and progress over time to more frequent drinking and heavier intake per occasion. During their early twenties, the differences between "prealcoholics" and individuals not so predisposed could be obscured by the heavy intake of the average person. At the critical stage in the mid-twenties to thirties, where the average drinker is cutting down, the alcoholic begins to become more apparent through continued high intake and resulting life difficulties. The heavier the genetic loading toward alcoholism and the less intense the environmental factors which might protect one from developing alcohol abuse, the earlier the onset of alcoholism and the more pervasive the alcohol problems are likely to be.

This level of biological predisposition must, of course, interact with the social and psychological environment. Thus, a person carrying the relatively light biological predisposition who is raised in a stable family where abstention or moderate drinking is emphasized and who only experiences periods of stress in the presence of a generally supportive environment may never demonstrate alcoholism. Another person, with the same level of biological predisposition, however, who has a very tumultuous late adolescence, or who lives in a location where alcohol is readily available, or who in the early thirties to mid-thirties goes through a serious life stress such as a divorce will be much more likely to demonstrate alcoholism despite the level of genetic loading.

In adequately evaluating the possible genetic causes of alcoholism, it is necessary to recognize that not everyone who becomes an alcoholic will have an obvious family history of the disorder. In some instances, alcoholism may appear to "skip" a generation if, for example, the son of an alcoholic chooses not to drink or places heavy restrictions on alcohol intake to avoid his father's problems (an example of environmental factors overriding a genetic propensity), while his son (i.e., the grandson of an alcoholic), having no warning about alcoholism, attempts to drink like everyone else only to end up an alcoholic. In other instances, a family history of alcoholism could be hidden because the father or mother had already recovered from alcoholism by the time the child was old enough to observe what was going on. Finally, alcoholism must begin somewhere in a family line, and the alcoholic patient might be the first person in a family with the necessary genetic combination

to raise the biological propensity for alcoholism beyond the necessary threshold for expression in that particular environment.

Similar hypothetical mechanisms can be invoked for other substances of abuse. Because the data to date are inconsistent, i favor the hypothesis that the biological factors involved in the propensity toward alcoholism are different from those predisposing toward analgesic or opiate abuse. Polydrug misuse (i.e., abuse of multiple substances other than alcohol or opiates) may be either a separate entity or just the prodromal phase for individuals who are likely to go on to opiate misuse or alcoholism. Of course, an opiate abuser who cannot obtain heroin is likely to misuse alcohol temporarily until the preferred drug is available (perhaps in an effort to treat some protracted abstinence symptoms) (Schuckit 1979a; Green and Jaffe 1977). One cannot rule out the possibility that if both alcoholism and heroin abuse are polygenically influenced disorders, the two problems might have a number of influential genes in common. However, the dissimilarities in age of onset and natural history of these two types of problems lead me to feel that the clearest research approach and hypothetical concept would be to look for different genetic factors for the misuse of separate drugs.

AVAILABILITY AND PRONENESS THEORY

(p. 46)

Smart

The theory generally predicts a gradual movement from use to abuse or addiction when both proneness and availability allow it. "Abuse," or use with harmful physical or social consequences, is most likely for the heaviest users or those with the greatest initial proneness and availability. Abuse resulting in criminality should also occur when physical or economic availability is low. These points should see a turning to acquisitive crime in order for the drug to be obtained. As true addiction is developed, proneness will lose its original importance, and availability will determine usage. In general, proneness is most important in the early experimental, heavy-use, and nonaddicted phases.

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The factors that account for continuation of substance use also contribute to the escalatory process. There are, however, important additional processes that promote the escalation. During the relatively early phases of escalation, consciously recognized dangers associated with substance use can facilitate rather than inhibit use if those dangers are experienced as more exhilarating than anxiety-provoking; if the self-initiated risks bring the user status and social approval; or if the user pits any perceived dangers against his or her competence and self-control, and then treats the matter as a contest which he or she is sure to win. As long as the user continues to perceive the overall gain as greater than the overall cost, use will continue; and the risk of escalation to more dangerous levels of use becomes more likely.

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