Scientists no longer believe that a drug has a simple physiological action, essentially the same in all humans. Experimental, anthropological, and sociological evidence has convinced most observers that drug effects vary greatly, depending on the physiology and psychology of the persons taking them, on their state when they ingest the drug, and on the social situation.
We can understand the social context of drug experiences better by showing how the nature of the experience depends on the amount and kind of knowledge available to the person taking the drug.
Since distribution is a function of the social organization of the groups in which drugs are used, drug experiences differ with differences in social organization.
This paper will focus primarily on the illegal use of drugs for pleasure--and especially the use of LSD and marijuana--but will also discuss the use of medically prescribed drugs by patients, and the involuntary ingestion of drugs by victims of chemical warfare.2
Drug effects vary from person to person and place to place because they almost always have more than one effect. People may conventionally focus on and recognize only one or a few of these effects, ignoring the others as irrelevant.
For example, most people think the effect of aspirin is to control pain; some know that it also reduces fever; few think of gastric irritation as a typical effect, although it is.
Thus users are likely to focus on the “beneficial” effects they seek and to ignore others.2
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1 This paper, prepared by Jean B. Wilson and reviewed by Howard S. Becker, consists of material taken from two previously published articles written by Dr. Becker. (1) “Consciousness, Power and Drug Effects,” Journal of Psychedelic Drugs 6 (1974): 67-76. Reprinted with permission of STASH, Inc. Copyright © 1974. (2) “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug-Induced Experiences,” Journal of Health and Social Behavior 8(1967):163-176. Reprinted with permission of the American Sociological Association.
2 Material in this paragraph was taken from “Consciousness, Power and Drug Effects,” p. 67. See footnote 1.
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DRUG EFFECTS, KNOWLEDGE, AND SOCIAL STRUCTURE
When people take drugs, their subsequent experience is likely to be influenced by their ideas and beliefs about the drug (Becker 1967). What they know about the drug influences the way they use it, the way they interpret its manifold effects and respond to them, and the way they deal with the aftereffects.
Conversely, what they do not know also affects their experience, making both certain interpretations and action, based on that missing knowledge, impossible. (I use “knowledge” to refer to any ideas or beliefs about a drug that anyone concerned in its use, e.g., illicit drug sellers, physicians, researchers, or lay drug users, believes to have been tested against experience and thus to carry more weight than mere assertions of faith.)2
DOSAGE
Many drug effects are dose related. The drug has one set of effects if you take X amount and quite different if you take 5X. Similarly, the effects vary depending on the means of taking a drug.
How much of a drug you take and how you take it depend on what you have learned from sources you consider knowledgeable and trustworthy.3 Most people know, for instance, that the usual dose of aspirin tablets is two and that they should be swallowed. On the other hand, few people have readily available knowledge about the vast majority of drugs prescribed by doctors or about those illicitly obtained, such as LSD.
Persons planning to take a drug (for whatever reason) either resort to trial-and-error experimentation or rely on sources they consider reliable (scientists, physicians, or more experienced drug users). These sources can usually tell the prospective user how much to take and how to take it to achieve whatever the desired effect may be (to control blood clotting time, to get high, or whatever).3
With the understanding thus acquired, users take an amount whose effect they can more or less accurately predict. They usually find this prediction confirmed, though the accuracy of conventional knowledge needs to be known. In this way, their access to knowledge exerts a direct influence on their experience, allowing them to control the physiological input to that experience.3
This analysis supposes that users have complete control over the amount they take. This is not always true, since a user may wish to take more than the physician will prescribe or a pharmacist sell.
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2 Material in these paragraphs was taken from “Consciousness, Power and Drug Effects,” p. 67. See footnote 1.
3 Material in these paragraphs was taken from “Consciousness, Power and Drug Effects.” pp. 67-68. See footnote 1.
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On the other hand, doctors ordinarily prescribe and pharmacists sell amounts larger than recommended for one-time use, so that users can take more than they are “supposed to.” They can also purchase drugs illicitly or “semilicitly” (e.g., from a friendly neighborhood pharmacist).3
MAIN EFFECTS
Social scientists have shown how the definitions drug users apply to their experience affect that experience. Persons suffering opiate withdrawal will respond as “typical” addicts if they interpret their distress as opiate withdrawal, but not if they blame the pain on some other cause (e.g., recovery from surgery).
Marijuana users must learn to interpret its subtle effect as being different from ordinary experience and as pleasurable before they “get high” (Becker 1953). Native Americans and Caucasians interpret peyote experiences differently (Aberle 1966), and LSD trips have been experienced as consciousness expansion, transcendental religious experience, mock psychosis, or being high (Blum and Associates 1964).
In short, users bring to bear, in interpreting their experience, knowledge and definitions derived from participation in particular social groups.4
SIDE EFFECTS
Side effects are not a medically or pharmacologically distinct category of reactions to drugs. Rather, they are effects not desired either by the user or the person administering the drug. Both side effects and main effects are thus socially defined categories.
Mental disorientation might be an unwanted side effect to a physician but a desired main effect for an illicit drug user.4 A drug user’s knowledge, if adequate, lets him or her identify unwanted side effects and deal with them in a self-satisfactory way.
Users concentrating on a desired main effect may not observe an unpleasant side effect or may not connect it with use of the drug. They interpret their experience most adequately if those who prepare them for the drug’s main effects likewise teach them the likely side effects and how to deal with them.
Illicit drug users typically teach novices the side effects to look out for, give reassurance about their seriousness, and give instructions in how to avoid or overcome them.5
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3 Material in this paragraph was taken from “Consciousness, Power and Drug Effects,” pp. 67-68. See footnote 1.
4 Material in these paragraphs was taken from “Consciousness, Power and Drug Effects,” pp. 68-69. See footnote 1.
5 Material in this paragraph was taken from “Consciousness, Power and Drug Effects,” p. 69. See footnote 1.
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LSD
The peculiar effects that lysergic acid diethylamide (LSD-25) has on the mind were discovered in 1938 by Albert Hoffman, who synthesized the drug in 1943. Following World War II, it came into use in psychiatry, both as a method of simulating psychosis for clinical study and as a means of therapy (Unger 1966), and has been the subject of controversy ever since.
At one extreme, Timothy Leary considers its use so beneficial that he has founded a new religion in which it is the major sacrament. At the other extreme, psychiatrists, police, and journalists allege that LSD is extremely dangerous, that it produces psychosis, and that persons under its influence are likely to commit acts dangerous to themselves and others that they would not otherwise commit.
In spite of the great interest in the drug, I think it is fair to say that the evidence of its danger is by no means decisive (Cohen 1960; Cohen and Ditman 1962, 1963; Frosch et al. 1965; Hoffer 1965; Rosenthal 1964; Ungerleider et al. 1966).
If the drug does prove to be the cause of a bona fide psychosis, it will be the only case in which anyone can state with authority that they have found the unique cause of any such phenomenon. But if we refuse to accept the explanations of others, we are obligated to provide one of our own.
In what follows, I will consider the reports of LSD-induced psychoses and try to relate them to what is known of the social psychology and sociology of drug use. By keeping in mind what is known of the influence that knowledge and social orientation have on the effects--both main effects and side effects--that a drug user experiences, I hope to add both to our understanding of the current controversy over LSD and to our general knowledge of the social character of drug use.
In particular, I will make use of a comparison between LSD use and marijuana use. The early history of marijuana use contains the same reports of “psychotic episodes” now current with respect to LSD. But reports of such episodes disappeared at the same time as the number of marijuana users increased greatly. I must add a cautionary disclaimer.
I have not exhaustively examined the literature on LSD. What I have to say about it is necessarily speculative with respect to its effects; what I have to say about the conditions under which it is used is also speculative, but is based in part on interviews with a few users.
The physiological effects of drugs can be ascertained by standard techniques of physiological and pharmacological research.
In contrast, the subjective changes produced by a drug can be ascertained only by asking the subject how he or she feels. People who take drugs for recreational purposes do so because they wish to experience just those subjective effects which they would either ignore or define as noxious side effects if they were taking a drug for medicinal reasons.
And because the use of drugs to induce a change in consciousness seems to many immoral, drug users come to the attention of sociologists as lawbreakers. Nevertheless, some sociologists, anthropologists, and social psychologists have investigated the problem of drug-induced subjective experience in its own right.
Taking their findings together the following conclusions seem justified (Becker 1963; Blum and Associates 1964;[6] Lindesmith 1947; Metzner et al. 1965; Aberle 1966; Schachter and Singer 1962; Nowlis and Nowlis 1956).
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[6] Material on this page was taken from “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug-Induced Experiences.” See footnote 1 .
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(1) Many drugs, including those used to produce changes in subjective experience, have a great variety of effects, and the user may be unaware of some of them, or may not recognize them as attributable to use of the drug.
(2) The effects of the same drug may be experienced differently by different people or by the same people at different times.
(3) Since recreational users take drugs in order to achieve some subjective state not ordinarily available to them, they expect and are most likely to experience those effects which are different from ordinary patterns. Thus, distortions in perception of time and space and shifts in judgment of the importance and meaning of ordinary events are the most commonly reported effects.
(4) Any of a great variety of effects may be singled out by the user as desirable or pleasurable. Even effects which seem to the uninitiated to be uncomfortable, unpleasant, or frightening--perceptual distortions or visual and auditory hallucinations--can be defined by users as a goal to be sought (Becker 1963).
(5) How people experience the effects of a drug depends greatly on the way others define those effects for them (Becker 1963; Blum and Associates 1964; Lindesmith 1947; Metzner et al. 1965; Aberle 1966; Schachter and Singer 1962; Nowlis and Nowlis 1956).
If others whom users believe to be knowledgeable single out certain effects as characteristic and dismiss others, they are likely to notice those same effects as characteristic of their own experience.
If certain effects are defined as transitory, users are apt to believe that those effects will go away. The scientific literature and, even more, the popular press frequently state that recreational drug use produces a psychosis.
What writers seem to mean by “psychosis” is a mental disturbance of some unspecified kind, involving hallucinations, an inability to control one’s stream of thought, and a tendency to engage in socially inappropriate behavior
In addition, and perhaps most important, psychosis is thought to be a state that will last long beyond the specific event that provoked it. Verified reports of drug-induced psychoses are scarcer than one might think (Cohen 1960; Cohen and Ditman 1962, 1963; Frosch et al. 1965; Hoffer 1965; Rosenthal 1964; Ungerleider et al. 1966; Bromberg 1939; Curtis 1939; Nesbitt 1940).
Nevertheless, let us assume that these reports represent an interpretation of something that really happened. What kind of event can we imagine to have occurred that might have been interpreted as a “psychotic episode”?
The most likely sequence of events is this. An inexperienced user has certain unusual subjective experiences, which he or she may or may not attribute to having taken the drug, such as a distorted perception of space, so that it is difficult to climb stairs.
The user’s train of thought may be so confused that it is impossible to carry on a normal conversation. The user may suspect that the way he or she sees or hears things is quite different from the way others see and hear them. Whether or not the user attributes what is happening to the drug, the experiences are apt to be upsetting.
One of the ways we know that we are normal human beings is that our perceptual world seems to be6
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6 Material on this page was taken from “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug-Induced Experiences.” See footnote 1.
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pretty much the same as other people’s. If this is no longer true--if we find our subjective state so altered that our perceptions are no longer like other people’s, we may think we have become insane.
This is precisely what may happen to the inexperienced drug user. Moreover, this interpretation implies that the change is irreversible or, at least, that normality is not going to be restored easily.
The drug experience, perhaps originally intended as a momentary entertainment, now looms as a momentous event which will disrupt one’s life, possibly permanently. Faced with this conclusion, the user develops a fullblown anxiety attack, but it is an attack caused by the reaction to the drug experience rather than a direct consequence of the drug itself.
(It is interesting that, in published reports of LSD psychoses, acute anxiety attacks appear as the largest category of untoward reactions [Frosch et al. 1965; Cohen and Ditman 1963; Ungerleider et al. 1966; Bromberg 1939].)
Of course, long-time users may have similar experiences if they take a higher dosage than they are used to or because illicitly purchased drugs may vary greatly in strength. The scientific literature does not report any verified cases of people acting on their distorted perceptions so as to harm themselves or others, but such cases have been reported in the press.
If users have, for instance, stepped out of a second story window, deluded into thinking it only a few feet to the ground (Cohen 1960; Hoffer 1965). it would be because they had failed to make the necessary correction for the drug-induced distortion rather than because of an anxiety attack.
Experienced users assert, however, that such corrections can be made and that they can control their thinking and actions so as to behave appropriately (Becker 1963).
Thus the most likely interpretation we can make of the drug-induced psychoses reported is that they are either severe anxiety reactions to an event interpreted and experienced as insanity, or failures of the user to correct for the perceptual distortions caused by the drug. While there are no reliable figures, it is obvious that a very large number of people use recreational drugs, primarily marijuana and LSD.
One might suppose, then, that a great many people would have disquieting symptoms and that many would decide they had gone crazy and thus have a drug-induced anxiety attack. But while there must be more such occurrences than are reported in the professional literature, it is unlikely that there are any large number.
Since the psychotic reaction stems from a definition of the drug-induced experience, the explanation of this paradox must lie in the availability of competing definitions of the subjective states produced by drugs.
Competing definitions come to users from other users who are known to have had sufficient experience with the drug to speak with authority. New users know that the drug does not produce permanent disabling damage in all cases, for they can see that other users do not suffer from it.
The question remains, of course, whether the drug may not produce damage in some cases, however rare, and whether a particular person may be one of those cases.6
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6 Material on this page was taken from “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug-Induced Experiences.” See footnote 1.
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When users experience disturbing effects, other users typically assure them that the change in their subjective experience is neither rare nor dangerous. They may, for instance, know of an antidote for the frightening effects.
They talk reassuringly about their own experiences, “normalizing” the frightening symptom by treating it as temporary. They maintain surveillance over affected users, preventing any physically or socially dangerous activity.
They show them how to allow for the perceptual distortion the drug causes and how to manage interaction with nonusers. They redefine the experience the novice is having as desirable rather than frightening, as the end for which the drug is taken (New York City Mayor’s Committee on Marihuana 1944; Becker 1963).
What they say carries conviction, because the novice can see that it is not some idiosyncratic belief but is instead culturally shared. He or she thus has an alternative to defining the experience as “going crazy,” and may decide that it was not so bad after all. We do not know how often this mechanism comes into play or how effective it is in preventing untoward psychological reactions.
However, in the case of marijuana, at least, the paucity of reported cases of permanent damage coupled with the undoubted increase in use suggests that it may be effective. For such a mechanism to operate, a number of conditions must be met. First, the drug must not produce permanent damage to the mind.
Second, users of the drug must share a set of understandings--a culture--which includes, in addition to material on how to obtain and ingest the drug, definitions of the typical effects, the typical course of the experience, the impermanence of the effects, and a description of methods for dealing with someone who suffers an anxiety attack because of drug use or attempts to act on the basis of distorted perceptions.
Third, the drug should ordinarily be used in group settings, where other users can present the definitions of the drug-using culture to the person whose inner experience is so unusual as to provoke use of the commonsense category of insanity.
Drugs for which technology and custom produce group use should produce a lower incidence of “psychotic episodes.”
The last two conditions suggest, as is the case, that marijuana, surrounded by an elaborate culture and ordinarily used in group settings, should produce few psychotic episodes.
I will discuss evidence on this point later. Users suffering from drug-induced anxiety may also come into contact with nonusers who will offer definitions, depending on their own perspective and experience, that may validate the diagnosis of “going crazy” and thus prolong the episode, possibly producing relatively permanent disability.
These nonusers include family members and police, but most important among them are psychiatrists and psychiatrically oriented physicians.”
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6 Material on this page was taken from “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug-Induced Experiences.” See footnote 1.
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Medical knowledge about the recreational use of drugs is spotty. Little research has been done or--as in the case of LSD--its conclusions are not clear, and what is known is not at the fingertips of physicians who do not specialize in the area.
Psychiatrists are not anxious to treat drug users, so few of them have accumulated any clinical experience with the phenomenon. Nevertheless, a user who develops severe and uncontrollable anxiety will probably be brought to a psychiatric hospital, to an emergency room where a psychiatric resident will be called, or to a private psychiatrist (Ungerleider et al. 1966).
Physicians, confronted with a case of drug-induced anxiety and lacking specific knowledge of its character or proper treatment, rely on a kind of generalized diagnosis.
They reason that people probably do not use drugs unless they are suffering from a severe underlying personality disturbance; that use of the drug may allow repressed conflicts to come into the open where they will prove unmanageable; that the drug in this way provokes a true psychosis; and, therefore, that the patient confronting them is psychotic.
Furthermore, even though the effects of the drug wear off, the psychosis may not, for the repressed psychological problems it has brought to the surface may not recede.
On the basis of such a diagnosis, the physician hospitalizes the patient for observation and prepares, where possible, for long-term therapy designed to repair the damage done to the psychic defenses or to deal with the conflict.
Both hospitalization and therapy are likely to reinforce the definition of the drug experience as insanity, for in both the patient will be required to “understand” that he or she is mentally ill as a precondition for return to the world (Szasz 1961).
Physicians, then, do not treat the anxiety attack as a localized phenomenon, to be treated in a symptomatic way, but as an outbreak of a serious disease heretofore hidden.
They may thus prolong the serious effects beyond the time they might have lasted had the user instead come into contact with other users. This analysis, of course, is frankly speculative; what is required is more study of the way physicians treat cases of the kind described and, especially, comparative studies of the effects of treatment of drug-induced anxiety attacks by physicians and by drug users.
A number of variables, then, affect the character of drug-induced experiences. It remains to show that the experiences themselves are apt to vary according to when they occur in the history of use of a given drug in a society.
In particular, it seems likely that the experience of acute anxiety caused by drug use will so vary. Let us suppose that someone in a society discovers, rediscovers, or invents a drug which has the ability to alter subjective experience in desirable ways.
This becomes known to increasing numbers of people, and the drug itself simultaneously becomes available, along with the information needed to make its use effective.
Use increases, but users do not have a sufficient amount of experience with the drug to form a stable conception of it.
No drug-using culture exists, and there is thus no authoritative alternative with which to counter the possible6
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6 Material on this page was taken from “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug-Induced Experiences.” See footnote 1.
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definition, when and if it comes to mind, of the drug experience as madness. “Psychotic episodes” occur frequently.
But individuals accumulate experience with the drug and communicate their experiences to one another. Consensus develops about the drug’s subjective effects, their duration, proper dosages, predictable dangers and how they may be avoided.
All these points become matters of common knowledge, available to the novice user as well as the experienced one. A culture exists. “Psychotic episodes” occur less frequently in proportion to the growth of the culture. Is this model a useful guide to reality? The only drug for which there is sufficient evidence to attempt an evaluation is marijuana.
Even there the evidence is equivocal, but it is consistent with the model. Marijuana first came into use in the United States in the 1920s and early 30s. and all reports of psychosis associated with its use date from approximately that period (Bromberg 1939; Curtis 1939; Nesbitt 1940)--before there was a fully formed drug-using culture.
The subsequent disappearance of reports of psychosis thus fits the model. It is, of course, a shaky index, for it depends as much on the reporting habits of physicians as on the true incidence of cases, but it is the only thing available. The psychoses described also fit the model, insofar as there is any clear indication of a drug-induced effect.
The best evidence comes from the 31 cases reported by Bromberg. Where the detail given allows judgment, it appears that all but one stemmed from the person’s inability to deal with either the perceptual distortion caused by the drug or with the panic created by the thought of losing one’s mind (Bromberg 1939, pp. 6-7).
The evidence cited is extremely scanty, which leaves the final question, then, whether the model can be used to interpret current reports of LSD-induced psychosis. Are these episodes the consequence of an early stage in the development of an LSD-using culture?
Will the number of episodes decrease while the number of users rises, as the model leads us to predict? We cannot predict the history of LSD by direct analogy to the history of marijuana, for a number of important conditions may vary, and evidence on a number of important factors is still highly inconclusive.
For example, there is a great deal of controversy as to whether or not LSD has any demonstrated causal relation to psychosis, apart from the definitions users impose on their experience.
My own opinion is that while LSD may be more powerful in its effects than other drugs that have been studied, the cases in the literature support the belief that most of the psychotic episodes are panic reactions to the drug experience occasioned by the users’ belief that they have lost their minds, or further disturbances among people already quite disturbed.
Is there an LSD-using culture? Here again, discussion must be tentative. It appears likely, however, that such a culture is in an early6
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6 Material on this page was taken from “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug-Induced Experiences.” See footnote 1.
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stage of development, and that users who are part of that culture are helped to cope with their experiences. For example, the notion that a “bad trip” can be brought to a speedy conclusion by taking Thorazine has spread.
Knowledge of other safeguards is also becoming more widely known. Insofar as this emergent culture spreads so that most or all users share the belief that LSD does not cause insanity, the knowledge about dosage, effects, and so on, as well as the incidence of “psychoses” should drop markedly or disappear.6
On the other hand, the ease with which LSD can be taken may negate the helpful influence of an LSD culture. No special paraphernalia is necessary, no special technique.
A sugar cube can be swallowed without instruction. Consequently it is possible that many people will take the drug without having acquired the presently developing cultural understanding, that many users will be people with no previous experience of recreational drug use, and that they will take it without the presence of supportive, experienced users.
Changing mores about youth use may add to the number of people who take the drug without being indoctrinated in the new cultural definitions, in which case the number of episodes may go up.6
We have been talking of drug use in which taking the drug is a matter of choice and in which the desired effect is a subjective one. But people also delegate control of their drug use to others, most commonly to physicians. When people take drugs prescribed to them by doctors, they do not rely on trial and error or a drug culture for knowledge concerning dosage, main effects, and side effects, but usually on the doctor.
While the doctor wants to alleviate some dangerous condition the patient is suffering from, doctor’s and patient’s desires do not necessarily coincide. Moreover, the doctor may not give patients sufficient information to anticipate the effects a drug may have, with the result that patients are sometimes unnecessarily frightened or may suffer dangerous reactions without connecting them with the drug.
The doctor may not give patients all the information he or she has for fear that the patient will disobey orders (Lennard 1972). Sometimes the doctor does not have adequate information about the experience the drug will produce. In either case, the drug experience is amplified and the chance of serious pathology increases.
The patient, not knowing what is likely to happen, cannot recognize the event when it occurs and cannot respond adequately or present the problem to an expert who can provide an adequate response.7
CONTROL BY EXTERNAL AGENTS
People sometimes find themselves required to ingest drugs involuntarily. In some instances, the agent administers the drug believing it to be for the good of the patient, as when a doctor gives medicine to a baby. who cannot resist.
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6 Material in these paragraphs was taken from “History, Culture and Subjective Experience: An Exploration of the Social Bases of Drug- Induced Experiences.” See footnote 1 .
7 Material in this paragraph was taken from “Consciousness, Power and Drug Effects,” pp. 71-72. See footnote 1.
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Or the agent may administer drugs “for the good of the community,” as when people with tuberculosis or leprosy are medicated to prevent them from infecting others (Roth 1963).8
But sometimes the external agent’s purposes conflict directly with those of the user, as when people find themselves the victims of chemical warfare. Those who administer drugs to involuntary users are either indifferent about providing recipients with any knowledge about it or actively attempt to prevent them from getting that knowledge.
Where destruction or incapacitation of the target population is the aim, the agent may try to conceal the fact that a drug is being administered. In this way, the agent hopes to prevent the taking of countermeasures and, in addition to the drug’s specific physiological effects, create panic at the onslaught of the unknown.8
CONCLUSION
If drug experiences somehow reflect or are related to social settings, we must specify the settings in which drugs are taken and the specific effect of those settings on the experiences of the participants.
This analysis suggests that it is useful to look at the role of power and knowledge in those settings: knowledge of how to take the drugs and what to expect when one does, and power over their distribution, the acquisition of information about them, and the decision to take or not to take them.
The need for further research extends both to the licit and illicit use of drugs, to the danger of taking drugs for recreational purposes (including “prescribed” drugs), into the profit orientation of pharmaceutical manufacturers, and to the sometimes inadequate knowledge and sometimes ambivalent motives of doctors who share or do not share their knowledge with their patients.9
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8 Material in these paragraphs was taken from “Consciousness, Power and Drug Effects,” pp. 74-75. See footnote 1. 9Material in this paragraph was taken from “Consciousness, Power and Drug Effects,” p. 75. See footnote 1.
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From N.I.D.A. Monograph 30 - Theories on Drug Abuse: Selected Contemporary Perspectives. [Page for pdf download, which includes diagrams and reference list.]