Internal Stimulus Control and Subjective Effects of Drugs

For many years psychotropic drugs have been characterized and classified using methods designed to measure their subjective effects in humans (). This research approach has two principal purposes: 1) to investigate the efficacy of a drug in attenuating unwanted subjective states in patients (e.g., pain, anxiety, depression), 2) to investigate the abuse potential of new drugs by comparing their subjective effects in experienced drug abusers to those produced by known drugs of abuse. In regard to the latter, such methods have been used to determine whether there are any common subjective states produced by all drugs of abuse (e.g., euphoria). Systematic studies of subjective methods for drug classification have been conducted at the Addiction Research Center (ARC) in Lexington, Kentucky, now part of the National Institute on Drug Abuse. A major mission of the ARC has been to evaluate new analgesic compounds to determine whether they produced morphine-like effects. The subjective effects of morphine and related compounds were an important aspect of this evaluation. The research demonstrated that morphine and related narcotic analgesics produced a unique spectrum of subjective effects that can be reliably discriminated Read more […]

History of Drug Exposure as a Determinant of Drug Self-Administration

The purpose of this paper is to review how a drug’s effectiveness in initiating and maintaining self-administration can be influenced by a subject’s past experience with drugs. Drug self-administration by humans and laboratory animals is considered an instance of operant behavior (), controlled by the subject’s genetic constitution, past history, and the current circumstances of drug availability (of Skinner, 1938). The influence of history of drug exposure on current drug-maintained behavior may be controlled, in turn, by the particular drugs and doses employed and the conditions under which the drug is administered. This discussion will focus on the ways in which a history of drug exposure can control later drug self-administration in laboratory animals. Effects of history of drug exposure on initiation of drug self-administration In order to study drug self-administration by laboratory animals, an experimenter must set up a situation in which subjects are exposed to some contingency between the occurrence of a specific response and delivery of a particular drug. For many drugs, no explicit behavioral or pharmacologioal history is necessary for the drug to maintain behavior. In one initial study, for example, Read more […]

Club Drugs and Hallucinogens

The term club drugs comes from the association of several drugs with use in dance clubs or all night dance parties (“raves”). Popular club drugs are methamphetamine (see earlier section, “Amphetamine-Related Disorders”), lysergic acid diethylamide (LSD; “acid”), 3,4-methylene-dioxymethamphetamine (MDMA; “Ecstasy” or “X”), gamma-hydroxybutyrate (GHB; “liquid X”), ketamine (“special K”), Rohypnol (“roofies”), and dextromethorphan (“DMX”) (). Emergency department visits due to MDMA and GHB use increased dramatically starting in the late 1990s. In the United States in 2002, emergency department visits for MDMA-related disorders numbered 4,026 and for GHB-related disorders numbered 3,330. Hallucinogenic drugs include LSD, mescaline, psilocybin, and synthetic derivatives such as 3,4-methylenedioxyamphetamine (MDA). The popularity of hallucinogens began to wane in the mid-1970s, but a modest resurgence in use occurred in the early 1990s, particularly among youth. MDMA (“Ecstasy”) MDMA, called “Ecstasy,” was promoted in the 1960s and 1970s as a “mood drug” without the distracting perceptual changes of other hallucinogens. MDMA is usually taken orally but can be taken in-tranasally (snorted). The purity of the drug in tablets Read more […]

Benzodiazepine Dependence: Animal Studies

Animal models are available for the production of both psychological and physical dependence. The most important animal model for the study of psychological dependence is the operant model using an intravenous self-administration technique originally used for opiate studies (see for example references-) . The animal is trained to self-administer the drug solution through an indwelling cannula by pressing a bar which activates the injection pump. The literature, particularly that relating to opiates has been extensively reviewed and is beyond the scope of this paper. These studies have shown that different groups of drugs have different levels as operant reinforcers. Thus opiates, amphetamines and cocaine are highly potent, ethanol and barbiturates moderately so and mescaline and phenothiazines relatively ineffective. Not all animals of the same species respond to reinforcement in the same way but some develop drug intake patterns which, like those of dependent humans, lead to physical illness and gross withdrawal reactions. In such experiments benzodiazepines have shown negligible evidence of dependence production. Thus Findley, Robinson and Peregrino studied the effect of intravenous administration of chlordiazepoxide Read more […]

Types of Drug Dependence

The WHO expert committee has recognized that different groups of drugs produce different types of dependence and that the type should be specified. The currently accepted types, the main classes of drugs involved and the clinical characteristics of the dependence are shown in Table Dependence types currently recognized and their clinical features. Apart from noting the great variety of types that are now recognized, the majority of classes can be ignored for the purpose of the present paper and attention can be concentrated on the groups of ethanol and barbiturate/sedative. There are still divergent opinions on whether they should be grouped together, for both show psychological and physical dependence with virtually identical withdrawal reactions, or whether they should be separated. In favour of their being put into a single group is the extensive cross tolerance that can occur among drugs with similar actions, regardless of chemical structure, and the partial effectiveness of one group in ameliorating the withdrawal effects of the other. Thus, for example, severe ethanol withdrawal reactions can be prevented by barbiturates, phenothiazines, benzodiazepines, chloral hydrate and paraldehyde. Conversely ethanol Read more […]

A Strange Class of Drugs

Hallucinogens are drugs that, when ingested, trigger a variety of strange and unpredictable sensations and experiences. Normally, such bizarre perceptions are experienced only in dreams, during periods of extreme emotional and physical stress, or as part of severe mental disorders such as schizophrenia. Psychoactive Chemicals There are dozens of different types of hallucinogens, some of which are produced naturally by plants and some of which are synthesized in laboratories or other facilities. There are many different hallucinogens used today, but the best known are mescaline and psilocybin, which come from plants, and LSD, ecstasy, and ketamine, which are manufactured in laboratories. What these drugs have in common is an ability to alter the functioning of the brain in such a way as to either modify the user’s perceptions or create entirely artificial perceptions. Users of hallucinogens experience a range of odd sensations, from mild distortions of information affecting the senses of sight, hearing, smell, taste, and touch to highly animated and dramatic sensory distortions — the hallucinations that give this class of drugs its name. Altered Perceptions Typically, users of hallucinogens characterize these sensations Read more […]


Unlike altered perceptions, which are triggered by some sort of external stimulus, hallucinations are sensations that people experience when there is no external stimulus. A hallucination can be experienced through any of the five senses. Hallucinations can sometimes be dramatic and complex, and as a result they can be quite frightening. Those who have taken large doses of hallucinogens often report experiencing bizarre and impossible events. For example, some users witness inanimate objects or people morphing into animals, objects talking and moving around a room, or extraterrestrial beings visiting from outer space. Others claim to have interactions with dead people. As bizarre as these drug-induced hallucinations can be, there are some features of hallucinations that are commonly experienced. Users often report walls flexing back and forth to the rhythm of music, straight lines curving and then straightening out, and objects appearing and then disappearing from view. In an interview, a college student recalled this LSD experience: We went to the sink that had little droplets of water in the bottom of it. By “unfocusing” our attention, we could cause strange effects to occur. The sink became this rushing current Read more […]

Hallucinogens: Addiction

Although most neurologists and pharmacologists report few lasting adverse physical effects from hallucinogen use, one concern among those who formulate the government’s drug policies is whether hallucinogens might be addictive. Of the scientific studies that have focused on this aspect of hallucinogens, none has concluded that they are addictive. This means that their prolonged use does not create a physiological craving or dependency based on changes in a user’s body chemistry. In addition, unlike drugs known to be addictive, there do not appear to be any physiological withdrawal symptoms or cravings when use of hallucinogens is terminated. Furthermore, unlike users of addictive drugs, users of hallucinogens typically do not have the urge to take their drugs many times a day. In fact, hallucinogenic experiences tend to be exhausting, and users report needing time to rest and recover following a trip. The use of hallucinogens more often than once a week is extremely rare; the majority of regular users report using them once a month or a few sporadic times in the course of a year. One of the reasons given for this low frequency of use is the long duration of a hallucinogen trip, which often lasts many hours. The Read more […]

Hallucinogens: Risks

Being nonaddictive does not mean hallucinogens are risk-free, however. Although the probability of death from the effects of a hallucinogen itself is low in comparison to narcotics such as heroin, health-care professionals warn that using hallucinogens can still have serious health consequences. There are no known deaths among humans because of brain, heart, or pulmonary failure that can be directly attributed to an overdose of any hallucinogen (although laboratory animals administered high doses of LSD have died from respiratory arrest). However, even though studies indicate that low doses of hallucinogens produce no long-lasting effects, high doses of hallucinogens have been known to cause severe psychotic breakdowns requiring long periods of psychiatric treatment. The danger of hallucinogens lies not in their toxicity but, rather, in the unpredictability of their psychological effects. For example, users have been known to wander down streets without knowing who they are or where they have been, or have walked in freezing weather without proper clothing, unaware that they were suffering from frostbite. Episodes of fatal consequences of hallucinogen use, mostly attributed to LSD, have been recorded. Pedestrians Read more […]

Hallucinogens and Spiritual Rituals

For thousands of years, people in many cultures have used hallucinogens in an attempt to gain spiritual insights to help them deal with the uncertainties that are part of their daily lives. They try to communicate with their deities to gain understanding and control over unpredictable events like birth, death, and illness. People in these cultures induce hallucinations by eating plants such as peyote and several species of mushrooms that naturally produce hallucinogenic chemicals. Botanists and ethnologists who have studied this use of hallucinogens refer to psychoactive plants used in religious rituals as entheogens, from the Greek word meaning “divinely inspired.” Ancient Use Archaeologists believe that hallucinogens were also used in a number of ancient societies to help leaders make important decisions relating to issues such as war, hunting, migrating to a new home, and selecting tribal and spiritual leaders. All of these situations were important enough to require consultation with a deity, who was believed to communicate with earthly beings while they were in a trance. Why entheogens were used in religious rituals in the first place is uncertain. But scholars studying these ancient cultures have a plausible Read more […]