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Drug Dependence


   Drug Dependence, psychological and sometimes physical state characterized by a compulsion to take a drug in order to experience its psychological effects. Addiction is a severe form of dependence, usually marked by physical dependence. The latter state exists when the drug has produced physiological changes in the body, as evidenced by the development of tolerance (when increasing amounts of the drug are needed to achieve the same effect), and of a withdrawal syndrome after the drug's effects have worn off. The syndrome is marked by such symptoms as nausea, diarrhoea, or pain; these vary with the type of drug. Psychological dependence, or habituation, is present when the compulsion to take a drug is strong, even in the absence of physical withdrawal symptoms.

Scientists often measure a drug's potential for abuse by studies with laboratory animals. Drugs that an animal will administer to itself repeatedly are said to have powerful reinforcing properties and a high potential for abuse. Examples include some of the major abused drugs—opium, alcohol, cocaine, and barbiturates. Other drugs, such as marijuana and the psychoactive drugs, appear to produce habituation in humans even though they are not powerful reinforcers for laboratory animals.

The drugs that are commonly abused, besides substances such as alcohol and tobacco, can be grouped into six classes: the opioids, sedative-hypnotics, stimulants, hallucinogens, cannabis, and inhalants.


The class of opioids includes drugs derived from opium (such as morphine and heroin) and its synthetic substitutes (such as methadone). Medically, morphine is a potent pain reliever; indeed, it is the standard by which other pain-relieving drugs are measured. It and other opium derivatives also suppress coughing, reduce movements of the intestine (providing relief from diarrhoea), and induce a state of psychological indifference. Heroin, a preparation synthesized from morphine, was introduced in 1898 as a cough suppressant and non-addicting substitute for morphine. The addictive potential of heroin was soon recognized, however, and its use was prohibited in many countries, even in medical practice. Users report that heroin produces a “rush” or a “high” immediately after it is taken. It also produces a state of profound indifference and may increase energy.

Opioids produce different effects under different circumstances. The drug taker's past experience and expectations have some influence, as does the method of administering the drug (by injection, ingestion, or inhalation). Symptoms of withdrawal include kicking movements in the legs, anxiety, insomnia, nausea, sweating, cramps, vomiting, diarrhoea, and fever.

During the 1970s, when scientists isolated substances called enkephalins, naturally occurring opiates in the brain, they discovered what many believe to be the reason behind physical dependence on opioids—that is, the drugs are thought to mimic the action of enkephalins. If true, this hypothesis suggests that physical dependence on the opioids may develop in those who have a deficiency of these natural substances.


The principal drugs of abuse in the class are of sedative-hypnotics are the barbiturates, which have been used since the early 1900s to relieve anxiety and induce sleep. They are also used medically in the treatment of epilepsy. Some abusers of the barbiturates ingest large amounts daily but never appear intoxicated. Others use the drugs for binges of intoxication, and still others use them to boost the effect of heroin. Many abusers, especially those of the first type, obtain their drugs routinely from general practitioners (GPs).

Barbiturates produce severe physical dependence; in this, as in their effects, they closely resemble alcohol. Abrupt withdrawal results in similar symptoms: shaking, insomnia, anxiety, and sometimes, after a day, convulsions and delirium. Death can occur when barbiturates are suddenly discontinued. Toxic doses—often little more than is required to produce intoxication—are often taken accidentally. Barbiturates are particularly dangerous when combined with alcohol.

Other sedative-hypnotics include the benzodiazepines, which are distributed under such names as Valium and Librium. These are the so-called minor tranquillizers that are used in the treatment of anxiety, insomnia, and epilepsy. They are generally safer than the barbiturates and are now commonly used instead of the older drugs, but tranquillizer addiction, in turn, has become a problem.


Commonly abused stimulants are cocaine and drugs of the amphetamine family. Cocaine, a white, crystalline powder with a bitter taste, is extracted from the leaves of the South American coca bush. It is used medically to produce anaesthesia for surgery of the nose and throat and to constrict blood vessels and reduce bleeding during surgery; but abuse, which increased considerably in the late 1970s, can lead to severe physiological and psychological problems. A highly addictive, smokable form of cocaine, “crack”, appeared in the 1980s.

Amphetamines, introduced in the 1930s for the treatment of colds and hay fever, were later found to affect the nervous system. For a while they were commonly used as an appetite suppressant by people trying to lose weight. Today their use is restricted primarily to the treatment of narcolepsy, a sleep disorder characterized by sudden sleep attacks throughout the day, and of hyperactivity in children, in whom amphetamines produce a calming effect. For adults, however, amphetamines rightfully earn their common name, “speed”. These drugs heighten alertness, elevate mood, and decrease fatigue and the need for sleep, but they often make users irritable and talkative. Both cocaine and amphetamines, after prolonged daily use, can produce a psychosis similar to acute schizophrenia.

A designer drug, 3,4-methylene dioxymethamphetamine, also know as Ecstasy or “E”, gives users a great sense of well-being; affection for all those around them; increased energy; and, sometimes, hallucinations. Associated with rave culture, its adverse effects can make users feel ill or experience a sense of loss of control, dehydration, and long-term memory and weight loss. There have been some deaths associated with taking Ecstasy and other drugs at raves.

Tolerance to both the euphoric and appetite-suppressing effects of amphetamines and cocaine develops rapidly. Withdrawal from amphetamines, particularly if the drug is injected intravenously, produces depression so unpleasant that the drug user has a powerful incentive to keep taking the drug until he or she collapses.



Hallucinogens are not used medically in most countries except occasionally in the treatment of dying patients, people with mental illness, drug abusers, and alcoholics. Among the hallucinogens that were widely abused during the 1960s are lysergic acid diethylamide, or LSD, and mescaline, which is derived from the peyote cactus. Although tolerance to these drugs develops rapidly, no withdrawal syndrome is apparent when they are discontinued.

Phencyclidine, or PCP, known popularly by such names as “angel dust” and “rocket fuel”, has no current use among human beings but is occasionally used by veterinary surgeons as an anaesthetic and sedative for animals. It became a common drug of abuse in the late 1970s, partly because it can easily be synthesized. Its effects are quite different from those of other hallucinogens. LSD, for example, produces detachment and euphoria, intensifies vision, and often leads to a crossing of senses (colours are “heard”, sounds are “seen”). PCP, by contrast, produces a sense of detachment and a reduction in sensitivity to pain; it may also result in either triggering or producing symptoms so like those of acute schizophrenia that even professionals confuse the two states. The combination of this effect and indifference to pain has sometimes resulted in bizarre thinking, occasionally marked by violently destructive behaviour.


The plant Cannabis sativa is the source of both marijuana and hashish. The leaves, flowers, and twigs of the plant are crushed to produce marijuana; its concentrated resin is hashish. Both drugs are usually smoked. Their effects are similar: a state of relaxation, accelerated heart rate, perceived slowing of time, and a sense of heightened hearing, taste, touch, and smell. These effects can be quite different, however, depending on the amount of drug consumed and the circumstances under which it is taken. Marijuana and hashish are not thought to produce psychological dependence except when taken in large daily doses. The drugs can be dangerous, however, especially when smoked before driving. Although the chronic effects are not yet clear, marijuana is probably injurious to the lungs in much the same way as tobacco. A source of concern is its regular use by children and teenagers, because the intoxication markedly alters thinking and interferes with learning. A consensus exists among doctors and others working with children and adolescents that use is undesirable and may interfere with psychological, and possibly physical, maturation.

Cannabis has been used as a folk remedy for centuries, but it has no well-established medical use today. Experimental work has been done using its active ingredient, delta-9-tetrahydrocannabinol (THC), for treating alcoholism, seizures, pain, the nausea produced by anticancer medications, and glaucoma. Its usefulness for glaucoma patients seems fairly certain, but its disorienting effects make its possible employment by cancer patients more doubtful.


   In the class of inhalants are substances that are not usually considered drugs, such as glue, solvents, and aerosols, such as cleaning fluids. Most such substances sniffed for their psychological effects act to depress the central nervous system. Low doses can produce slight stimulation, but in higher amounts they cause their users to lose control or lapse into unconsciousness. The effects, which are immediate, can last for as long as 45 minutes. Headache, nausea, and drowsiness follow. Sniffing inhalants can impair vision, judgement, and muscle and reflex control. Permanent damage can result from prolonged use, and death can result from sniffing highly concentrated aerosol sprays. Although physical dependence does not seem to occur, tolerance to some inhalants does develop. Another source of medical concern is the widespread misuse, for their supposed aphrodisiac effect, of so-called “poppers”—chemicals such as isoamyl nitrite that have legitimate medical functions as blood-vessel dilators. Continued sniffing of these substances can damage the circulatory system and have related harmful effects.


   With the exception of treatment of opioid dependence, medical attention to the problems of the drug abuser is largely confined to dealing with overdoses, acute reactions to drug ingestion, and the incidental medical consequences of drug use, such as malnutrition and medical problems caused by unsterilized needles. Abusers of barbiturates and amphetamines may require hospitalization for detoxification, as is common among alcoholics. Others, such as those arrested repeatedly for possession of marijuana, may, in lieu of imprisonment, be forced to undergo treatment designed primarily for opioid abusers. Whatever the substance abused, the goal of most treatment programmes is abstinence.

Two types of treatment programme are used for most opioid users. Therapeutic communities require the drug abuser to take personal responsibility for his or her problem. Typically, the idea behind this treatment is that the drug abuser is emotionally immature and must be given a second chance to grow up. Harsh encounters with other members of the community are typical; the support of others, together with status and privilege, are used as rewards for good behaviour.

The other model for opioid-abuse treatment is the use of heroin substitutes. One such substitute is methadone, which acts more slowly than heroin but is still addictive. The idea is to help the user gradually withdraw from heroin use while removing the need for finding the drug “on the street”. A more recent treatment drug, naltrexone, is non-addictive and acts by blocking the equivalent “high”; it also cannot be used by individuals with liver problems, which are common among addicts.

"Drug Dependence", Microsoft® Encarta® Encyclopedia 2001. © 1993-2000 Microsoft Corporation. All rights reserved.

Drug Dependence Reference:

Bakalar, James B., and Grinspoon, Lester. Drug Control in a Free Society. Cambridge University Press, 1984. Concise study, with bibliography.

Blaze-Gosden, Tony. Drug Abuse: the Facts about today's Drug Scene. Newton Abbot: David & Charles, 1987. Encouragement to the general reader to control drug abuse.

Coleman, Vernon. Addicts and Addictions. London: Piatkus; Corgi1986; 1987. . Informal advice from a doctor on the dangers of addiction.

Freemantle, Brian. The Fix. London: Joseph; Corgi1985; 1986. . Thorough study for the general reader on the drugs trade and drug abuse.

Leigh, Vanora. Drugs: Why say no?. London: Penguin, 1988. Reasons not to take drugs.

Mothner, Ira, and Weitz, Alan. How to Get off Drugs. Harmondsworth: Penguin, 1986. American work, revised and updated for the British market.

Orlandi, Mario, and others. Encyclopedia of Good Health: Substance Abuse. Facts on File, 1989. Outlines of main facts, anecdotes, questions to ask oneself.

Tyler, Andrew. Street Drugs. New English Library1988. . Revised and updated edition with substantial information for the general reader on the nature and dangers of street drugs.