Although use of alcohol, tobacco and illicit drugs has been declining, a significant percentage of the U.S. population uses at least one of these substances . Alcohol is the most commonly used psychoactive substance; in a 1992 survey, approximately 48 percent of the population surveyed had consumed alcohol in the past month and 26 percent smoked tobacco . Approximately 11 percent acknowledged using illicit drugs in the past 12 months (See Table 3 below) .
TABLE 3: Estimated Percentage of Illicit Drug Usage in the United States Population According to Gender, Age and Race
|Total Population||36.2 %||11.1 %||5.5 %
|Male||41.0 %||13.4 %||7.1 %
|Female||31.7 %||9.0 %||4.1 %
|12 - 17||16.5 %||11.7 %||6.1 %
|18 - 25||51.7 %||26.4 %||13.0 %
|26 - 34||60.8 %||18.3 %||10.1 %
|35 +||28.0 %||5.1 %||2.2 %
|Caucasians||37.7 %||11.3 %||5.5 %
|Hispanics||29.2 %||10.8 %||5.3 %
|African Americans||33.6 %||11.5 %||6.6 %
Source: National Household Survey on Drug Abuse: Population Estimates 1992 
The prevalence of heavy use in the general population - in terms of prevalence, heavy use appears to be more stable than mild or moderate use  has been the subject of many studies. The most recent and representative study was conducted in 1991 with a complex sample representing the entire noninstitutionalized U.S. population aged 15 to 54 years in the 48 contiguous states . Using face-to-face interviews to evaluate more than 8,000 people according to the DSM-III-R criteria for substance abuse or dependence, the investigators found a lifetime prevalence of approximately 7.5 percent for drug abuse or dependence and of approximately 27 percent for any substance-use disorder in persons between 15 and 54 years of age (See Figure 1 below). Less than half of those with substance abuse or dependence had ever received any treatment for these conditions.
FIGURE 1: Prevalence of substance abuse and dependence in the general population.
[Adapted from Kessler RC, McGonagle KA, Zhai S et al. Lifetime and 12 month prevalence of DSM-III-R psychiatric disorders in the United States: results from the National Comorbidity Survey. Arch Gen Psychiatry 1994; 51:8-19]
Although addictive disorders are widespread in the general population, their manifestations and the opportunities provided for specific interventions may vary widely among certain demographic groups. An understanding of these specifics is helpful for ensuring diagnosis and treatment.
Adolescents and Young Adults
Persons between 18 and 25 years of age are the most likely to use illicit drugs. The age at which an adolescent begins using alcohol and illicit drugs is a powerful predictor of later alcohol and drug problems, especially if use begins before age 15 .
Teenagers use alcohol and tobacco more than any other drug. The incidence of heavy use of alcohol defined as having five or more drinks in a row during the previous two weeks peaked at 41 percent among high school seniors in the early 1980s. Since then, it has dropped to 29.8 percent, which is still quite high .
Use of most illicit drugs by adolescents increased significantly in 1993, reversing the downward trend that had been observed for several years . Among high school seniors, the current lifetime prevalence of any illicit drug use is 42.9 percent, and the prevalence of any illicit drug use in the past year is 31 percent. In particular, use of marijuana, lysergic acid diethylamide (LSD) and inhalants increased in 1993. Current data indicate that marijuana has been used at least once by 12.6 percent of eighth graders and by 35.3 percent of high school seniors. About 3.5 percent of eighth graders and 10.3 percent of seniors have used LSD. Of particular concern is the finding that inhalants such as glues and solvents have been tried by 19.4 percent of eighth graders and by 17.4 percent of seniors. The powder form of cocaine has been used by 2.9 percent of eighth graders and 6.1 percent of seniors; crack has been tried by 1.7 percent of eighth graders and by 2.6 percent of seniors.
Typically, the adolescent whose drug involvement progresses to substance abuse begins with commercially available drugs such as alcohol and tobacco, progresses to using marijuana and goes on to using other drugs or combinations of drugs. For this reason, cigarettes and alcohol are sometimes called "gateway" drugs. Polydrug use is more common among adolescents than adults . Among tobacco smokers 12 to 17 years of age, twothirds have also used an illegal drug, and among those smoking more than one pack per day, fourfifths have used an illegal drug.
The leading cause of death among people between 15 and 24 years of age is violence, including accidents, homicides and suicides; many of these deaths can be attributed to the use of drugs and alcohol . Nevertheless, young people are rarely aware of or concerned about the dangers of drug abuse. This is typical of adolescents' attitudes toward most risky behaviors: they are unwilling to appreciate the long-term consequences of many of their actions, particularly when admonished by their parents or other authority figures. However, if a trusting therapeutic relationship has been established, the family physician may have a unique opportunity to advise the preadolescent or teenager on the dangers of substance abuse. Health guidance should be given annually to all adolescent patients to promote avoidance of tobacco, alcohol and other abusable substances .
During pregnancy, at least 25 percent of women use nicotine, and 5 to 8 percent are at risk for alcoholrelated prenatal problems; the prevalence of illicit drug use in pregnant women is unclear, but it appears to be lower than that of nicotine and alcohol use . Women who use drugs during pregnancy have increased rates of meconium staining, fetalmonitor abnormalities, precipitous delivery, abruptio placentae and premature delivery . Infants born to addicts may be more likely to have birth defects, because most addicted mothers also abuse alcohol, a known teratogen. Even occasional use of alcohol, tobacco or illicit drugs should be identified and discouraged in pregnant women.
It is particularly important to avoid fetal exposure to teratogens during the first trimester. However, if drug exposure has occurred, it is inappropriate to discontinue treatment efforts on the grounds that the "damage has already been done." Good nutrition and abstinence from drugs (except those prescribed by the physician) through the second and third trimesters often allow the fetus to "catch up" with normal growth and development, at least to some degree . Likewise, a nurturing and stimulating environment may provide similar benefits to the infant after birth.
Treatment of addicted pregnant women should include prenatal care, parenting and childbirth classes and home visits by public health nurses, as well as treatment of chemical dependence. However, referral to a treatment program is possible only when the physician is attuned to the signs of addiction in pregnant women. These may be elicited during careful history-taking and physical examination.
In addition, urinary toxicologic testing may be a useful means of confirming drug abuse suggested by findings in the history or physical examination, such as no or late prenatal care or the presence of multiple sexually transmitted diseases. Care should be taken so that urine testing does not initiate a cascade of events leading automatically to criminal penalties or loss of child custody. This can generally be achieved by handling urine specimens in the usual clinical way, which does not document the chain of custody required for legal evidence, and by physician advocacy for the benefit of the maternal-fetal unit and family.
Treatment of heroin addiction during pregnancy is particularly important. The street drug can produce wide swings in blood levels, from intoxication to withdrawal, that can lead to premature labor, spontaneous abortion and other severe adverse effects. In addition, heroin is often contaminated with teratogenic substances . The indicated treatment for heroin addiction during pregnancy is methadone maintenance, which produces a fairly constant and safe physiologic effect. Pregnancy increases methadone metabolism, and some patients require two doses per day to maintain stable blood levels as pregnancy progresses.
Infants born to mothers maintained with methadone may be physically dependent on opioids; however, they are not addicted and are easily treated in the nursery. Unmonitored intrauterine withdrawal is much more dangerous. While lower doses of methadone are less likely to cause withdrawal symptoms in the neonate, the most important dosing consideration is giving the patient an amount sufficient to prevent relapse to heroin, with all its associated risks to mother and fetus.
Prescribed methadone use is compatible with breast-feeding. However, maternal infection with HIV or human T-cell lymphotrophic virus I/II often precludes breast-feeding by women who have injected heroin.
With age comes a higher incidence of chronic painful physical disorders that may be treated with substances that have the potential for abuse. Vulnerability to addiction may be increased by feelings of anger, depression, anxiety, resentment at being dependent and frustration with deteriorating vision, hearing and agility . Undiagnosed chronic depression may predispose to benzodiazepine use and subsequent long-term abuse and addictive problems in later life .
Alcoholism in the elderly remains an underreported and often hidden disorder, despite increasing awareness of its detrimental effects. These include a high risk of alcohol-drug interactions. The elderly consume a disproportionate amount of prescription drugs and commonly use several prescription and over-the-counter medications concomitantly. Many of the medications the elderly are likely to take - including antidepressants and tranquilizers - interact with alcohol, often synergistically. Such interactions can result in aspiration pneumonia, falls, hip fractures or vehicular accidents .
Substance abuse is often misdiagnosed in elderly people, because such symptoms as changes in cognition, behavior or physical functioning tend to be misattributed to an underlying medical condition or simply old age. A thorough understanding of what constitutes normal age-related changes will help family physicians make the correct diagnosis .