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Pharmacology => Drug => Drug Dependce
Drug Dependce
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 , appear to produce habituation in humans even though they are not powerful reinforcers for laboratory animals.
The drugs that are commonly abused, except alcohol and tobacco, can be grouped into six classes: the opioids, sedative-hypnotics , see stimulants, hallucinogens, cannabis, and inhalants.
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 . 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.
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 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.
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.
HALLUCINOGENS
These drugs are not used medically in the United States except occasionally in the treatment of dying patients, the mentally ill, drug abusers, and alcoholics. Among the hallucinogens widely abused during the 1960s were 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 medical purpose for humans but is occasionally used by veterinarians as an anesthetic and sedative for animals. It became a common drug of abuse in the late 1970s, and is considered a menace because it can easily be synthesized. Its effects differ from those of other hallucinogens. LSD, for example, produces detachment and euphoria, intensifies vision, and often leads to a crossing of senses (colors are heard, sounds are seen). PCP, by contrast, produces a sense of detachment and a reduction in sensitivity to pain, and may trigger or produce symptoms so like those of acute schizophrenia that 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 behavior.
CANNABIS
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 differ, however, depending on the amount of drug consumed and the circumstances under which it is taken. Marijuana and hashish do not 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 have not been clearly determined, marijuana is probably injurious to the lungs in much the same way as tobacco. A cause for concern is the regular use by children and teenagers, because intoxication markedly alters thinking and interferes with learning. A consensus exists among physicians and others who work with children and adolescents that use of marijuana and hashish is undesirable and may interfere with psychological and possibly physical maturation.
Cannabis has been used as a folk remedy for centuries. Its active ingredient, delta-9-tetrahydrocannabinol (THC), has been used experimentally for treating alcoholism, seizures, pain, the nausea produced by anticancer medications, and glaucoma. Glaucoma patients have used THC successfully, but the disorienting effects limit its usefulness for cancer patients.
INHALANTS
This class includes substances that are usually not considered drugs, such as glue, gasoline, and aerosols like nasal sprays. Most such substances sniffed for their psychological effects depress the central nervous system. Low doses can produce slight stimulation, but higher amounts cause users to lose control or lapse into unconsciousness. The effects, which are immediate, can last as long as 45 minutes. Headache, nausea, and drowsiness follow. Sniffing inhalants can impair vision, judgment, 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 develops. Another source of medical concern is the widespread misuse, for a supposed aphrodisiac effect, of so-called "poppers"-chemicals such as isoamyl nitrite that have legitimate medical functions as blood vessel dilators (vasodilators). Continued sniffing of these easily obtainable substances can damage the circulatory system and have related harmful effects.
TREATMENT
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 programs is to foster abstinence in the patient.
Two types of treatment programs 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 behavior.
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 nonaddictive but does not provide an equivalent "high;" it also cannot be used by persons with liver problems, which are common among addicts.
SOCIAL ISSUES
Drug use for nonmedical purposes occurs throughout society. For this reason the 1978 President's Commission on Mental Health did not recommend health and mental-health assistance except to persons whose drug use was intense and compulsive. The commission identified heroin as the number one drug problem because heroin addiction may lead to criminal behavior to pay for the drug. Adding to the problem is the fact that chemically similar drugs can be synthesized and sold on the street because they are not yet classified as controlled substances.
In a 1995 household survey by the Substance Abuse and Mental Health Services Administration an estimated 12.8 million people in the United States classified themselves as current illicit drug users. Five in ten young adults (age 21 to 25) reported having tried illicit drugs at least once, while one in ten admitted current use. Almost 10 million Americans, 5 percent of the population over the age of 12 years, reported current use of marijuana. Another 5.6 million reported current use of illicit drugs other than marijuana. Despite a significant reduction in cocaine use since 1985, there were still an estimated 530,000 first-time users in 1994.
The survey identified education and employment status as important factors in illicit drug use. Young adults who had dropped out of high school had the highest rate of use (15.4 percent) while college graduates had the lowest rate of use (5.9 percent). More than 14 percent of unemployed adults were current illicit drug users in 1995, compared to 5.5 percent of employed adults. Among youths, the rate of illicit drug use among whites, blacks, and Hispanics was about equal.
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