Drug Dependence

I

Introduction

Drug Dependence, psychological and sometimes physical state characterized by a compulsion to use a drug to experience psychological or physical effects. Drug dependence takes several forms: tolerance, habituation, and addiction.

Tolerance, a form of physical dependence, occurs when the body becomes accustomed to a drug and requires ever-increasing amounts of it to achieve the same pharmacological effects. This condition is worsened when certain drugs are used at high doses for long periods (weeks or months), and may lead to more frequent use of the drug. However, when use of the drug is stopped, drug withdrawal may result, which is characterized by nausea, headaches, restlessness, sweating, and difficulty sleeping. The severity of drug withdrawal symptoms varies depending on the drug involved.

Habituation, a form of psychological dependence, is characterized by the continued desire for a drug, even after physical dependence is gone. A drug often produces an elated emotional state, and a person abusing drugs soon believes the drug is needed to function at work or home. Addiction is a severe craving for the substance and interferes with a person’s ability to function normally. It may also involve physical dependence.

Scientists often measure a drug’s potential for abuse by conducting studies with laboratory animals. Drugs that an animal administers to itself repeatedly are said to have powerful reinforcing properties and a high potential for abuse. These drugs include some commonly abused substances like opium, alcohol, cocaine, and see barbiturates. Other drugs, such as marijuana and the hallucinogens (see Psychoactive Drugs), appear to produce habituation in humans even though they are not powerful reinforcers for laboratory animals.

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The drugs that are commonly abused, except alcohol and tobacco, can be grouped into six classes: the opioids, sedative-hypnotics (see Sedative), see stimulants, hallucinogens, cannabis, and inhalants.

II

Opioids

This class includes drugs derived from opium, such as morphine and heroin, and 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 (see Narcotics). Morphine and other opium derivatives also suppress coughing, reduce movements of the intestine (providing relief from diarrhea), and induce a state of psychological indifference. Heroin, a preparation synthesized from morphine, was introduced in 1898 as a cough suppressant and nonaddictive substitute for morphine. The addictive potential of heroin, however, was soon recognized, and its use was prohibited in the United States, even in medical practice. Users report that heroin produces a “rush” or “high” immediately after being taken. It also produces a state of profound indifference and may increase energy.

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

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

III

Sedative-Hypnotics

The drugs most commonly abused in this class 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 people who abuse 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 effects of heroin. Many people who abuse these drugs, especially those who do so daily, routinely obtain the drugs from physicians.

Barbiturates produce severe physical dependence, closely resembling the dependence and effects produced by alcohol. Abrupt withdrawal results in similar symptoms: shaking, insomnia, anxiety, and sometimes, after a day, convulsions and delirium. Death can occur when use of barbiturates is suddenly discontinued. Toxic doses, which may be little more than what is required to produce intoxication, are often taken accidentally. Barbiturates are particularly lethal when combined with alcohol.

Other sedative-hypnotics include the benzodiazepines, which are marketed under such trade names as Valium and Librium. These are the so-called minor tranquilizers (see Tranquilizer) used in the treatment of anxiety, insomnia, and epilepsy. They are generally safer than the barbiturates and are now the preferred drug for treatment of these conditions. Consequently, tranquilizer addiction has become a problem.

IV

Stimulants

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 anesthesia for surgery of the nose and throat and to constrict blood vessels and reduce bleeding during surgery. Abuse of cocaine, which increased considerably in the late 1970s, can lead to severe physiological and psychological problems. A highly addictive, smokable form of cocaine called “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 people trying to lose weight commonly used them as appetite suppressants. Today, use is restricted primarily to the treatment of narcolepsy, a sleep disorder characterized by sudden sleep attacks during the day, and hyperactivity in children, for whom amphetamines produce a calming effect. For adults, however, amphetamines rightfully earn the street 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.

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

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