Summary by Faye Chao, MD CHAPTER
2

Based on “Principles of Addiction Medicine” Chapter by Rosa M. Crum, MD, MHS

SOME EPIDEMIOLOGIC PRINCIPLES

Epidemiology is the study of how diseases are distributed in populations as well as the study of the determinants of disease and health. Prevalence is the ratio of the total number of cases of a particular disease divided by the total number of individuals in a particular population at a specific time. Incidence refers to the occurrence of new cases of a disease divided by the total number at risk for the disorder during a specified period. Prevalence takes into account both the incidence and duration of a disease. Incidence is generally taken to represent the risk of the disease, whereas prevalence is an indicator of the public health burden the disease imposes.

Relative risk is the incidence of the disease among those with a particular characteristic divided by the incidence of the disease among those without exposure to that particular characteristic. Odds ratio is also a measure of the strength of association such as between a characteristic and disease. A relative risk or odds ratio >1 indicates a positive association of disease with a given characteristic, whereas <1 indicates a negative association.

Epidemiologic studies can be divided into two types: observational or experimental. Observational studies include cross-sectional, case–control, or cohort studies; in these types of studies, the investigator observes the study participants and gathers information for analysis. Experimental studies are designed by the investigator, study groups are selected, and an intervention is given to one group.

Throughout this chapter, the terms “substance abuse” and “substance dependence” are used alongside “substance use disorder” to reflect that the studies discussed were conducted prior to the change in nomenclature from “abuse” and “dependence” to “use disorder” that occurred with the release of the DSM-5 in 2013.

ALCOHOL USE DISORDERS

Prevalence

A number of major surveys in the United States and internationally have assessed the prevalence of addiction. Comparison of these studies sometimes is difficult because different measures and definitions of addiction are employed. One of the earliest surveys to assess the epidemiology of substance use disorders in the United States using structured psychiatric interview was the National Institute of Mental Health’s Epidemiologic Catchment Area (ECA) study, which was conducted between 1980 and 1984. For this study, more than 20,000 adults in five metropolitan areas were assessed using the Diagnostic Interview Schedule (using criteria from DSM-III). The National Comorbidity Survey (NCS) was first administered between 1990 and 1992 and assessed prevalence of abuse and dependence with a modified version of the Composite International Diagnostic Interview based on DSM-II-R criteria. The National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) was conducted from 2001 to 2002 and has provided lifetime and 12-month estimates of substance use disorders based on DSM-IV criteria using the Alcohol Use Disorder and Associated Disabilities Interview Schedule. The most current prior-year estimates of alcohol use disorders come from the annual National Survey on Drug Use and Health (NSDUH). Since 2000, the NSDUH has gathered information of prior-year prevalence of substance use disorders based on DSM-IV criteria.

Twelve-month prevalence of alcohol abuse from NESARC was 6.9% among men and 2.6% among women. For alcohol dependence, 12-month estimates were 5.4% for men and 2.3% for women. Lifetime prevalence of alcohol abuse and dependence was 17.8% and 12.5%, respectively. Data from the 2011 NSDUH indicate that 6.5% of the survey participants met criteria for alcohol abuse or dependence in the past year. Most studies found that the prevalence of alcohol use disorders is highest among young adults. Differences in estimates across surveys may be due to variations in the diagnostic instrumentation, the version of the DSM used, the size of the survey sample, and the locale of the survey participants.

Incidence

Prospective data gathered over time are less available; consequently, there is less information on incidence rates for substance use disorders in the general population. Generally, studies have found that the incidence of drinking problems is lower for women than for men and that the incidence for both men and women declines with age. One study found that women tended to develop problems associated with drinking later in life than men, and women were found to have higher rates of remission across all age groups than did men.

DRUG USE DISORDERS

Prevalence

Lifetime prevalence of drug abuse and dependence in the 2001–2002 NESARC survey were found to be 7.7% and 2.6%, respectively; the corresponding estimates for 12-month prevalence were 1.4% and 0.6%. Men generally were found to have a higher lifetime prevalence of drug use and drug use disorders overall in both the NESARC and the ECA. The NSDUH survey in 2011 found that the past-year prevalence of illicit drug use disorders was 2.5% overall, with the highest prevalence found among young adults aged 18 to 25. From the 2011 NSDUH, we know that 26.5% of the population reported current use of tobacco products, and data from the 2001–2002 NESARC indicate that 12.8% of the population met criteria for nicotine dependence in the prior year.

Incidence

There is a relative paucity of information regarding the incidence of drug use disorders as a group, with less information available for specific drugs. Early findings from the 1-year prospective ECA data showed that the incidence of illicit drug use disorders as a group is greater for men than for women across the entire life span. As was the case for alcohol-related disorders, the highest incidence for both men and women was found in the 18- to 29-year-old age group; incidence dropped sharply after young adulthood, and the incidence of drug use disorders among those 65 years of age and older was zero. More recent analyses of the 3-year prospective NESARC data showed annual incidence of drug abuse was 0.28 per 100 person-years and annual incidence of drug dependence was 0.32 per 100 person-years.

TRENDS OF ALCOHOL, TOBACCO, AND ILLICIT DRUG USE

Based on the most recent NSDUH completed in 2011, approximately half (51.8%) of the US population report current drinking (having at least one drink in the past month); over the past decade, the proportion of current drinkers remains essentially unchanged. Similarly, the rates of binge drinking and heavy drinking have not changed significantly from the 2002 to 2011 NSDUH (about 23% for binge drinking and 6% to 7% for heavy drinking). Among young adults ages 18 to 25, overall binge drinking has decreased slightly over the past decade (from 40.9% to 36.8%).

Use of tobacco products in general also has declined over the prior decade based on data from the NSDUH from a high of 30.4% prevalence in 2002 to the current low of 26.5%. The decline is more pronounced among adolescents aged 12 to 17, as shown in both the NSDUH and the Monitoring the Future (MTF) study.

Past-month illicit drug use has remained about the same over the past decade according to NSDUH data—8.3% in 2002 versus 8.7% in 2011. The most commonly used illicit substance is marijuana. New trends are continually being assessed by ongoing surveys and provide important information regarding trends of use over time as well as surveillance of newer substances such as synthetic marijuana.

REMISSION FROM SUBSTANCE USE DISORDERS

Remission varies by individual characteristics, and maintaining remission is also dependent on consumption patterns while in remission. Only a minority of individuals with substance abuse or dependence report using treatment services. Using data from the NESARC, Dawson and colleagues found that at 3-year follow-up, maintenance of successful recovery from alcohol dependence was greatest for abstainers.

CORRELATES AND SUSPECTED RISK FACTORS

Gender

Alcohol use disorders are more common among men than among women, though survey data in the United States over the past 20 years provide evidence that the gender gap for prevalence of alcohol use disorders is narrowing. In particular, a history of childhood abuse has been found to be a potential predictor of women’s risk for alcohol and drug use disorders. Men also have a higher prevalence and incidence of drug use disorders than do women. Gender differences vary by the specific substance and the age of use. For example, in the 2012 Monitoring the Future study, annual prevalence of some substances including inhalant, tranquilizer, and amphetamine use was higher for 8th grade girls than boys.

Age

Prevalence of alcohol use disorders is generally lower among older adults, possibly because the incidence decreases over the life span, the duration of the disorder is reduced, or some combination of the two factors. Prevalence and incidence rates for illicit drug disorders are highest among individuals in late adolescence and young adulthood. In general, the earlier the age of first use of alcohol or illicit drugs, the greater the estimated risk associated with the subsequent development of an alcohol or illicit drug use disorder.

Race and Ethnicity

The evaluation of race and its association with addiction is complex and sometimes conflicting. African American youth begin drinking at older ages and are less likely to develop abuse and dependence relative to Caucasians. However, African Americans tend to suffer more medical and social consequences from drinking. Prevalence of alcohol use disorders is also lower for Hispanics relative to Caucasians, yet alcohol dependence may be more persistent after it develops. Asian Americans generally have the lowest prevalence of alcohol use disorders in the United States, and Native Americans historically have had the highest. Less information is available for drug addiction. Data from the NCS show that African Americans and Hispanics are less likely to report lifetime drug use relative to Caucasians but are more likely to have persistent dependence once the disorder develops. Reports using data from the 2011 NSDUH indicate that the occurrence of past-year illicit drug use disorders was highest among Native Americans and lowest among Asian Americans. Similar relationships were documented in analyses of 12-month prevalence using the NESARC.

Family History

Alcohol disorders cluster in families and family history of dependence may predict the severity of the disorder in probands. Although many studies have indicated a possible genetic relationship for alcohol dependence, the association is complex. Evidence indicates that approximately half of the risk may be attributed to genetic influences, and environmental influences also have a major role. Analyses have also indicated associations of genetic liability to drug disorders involving multiple genetic risks.

Employment Status and Occupation

In the 2011 NSDUH findings, the proportion of alcohol use disorder was higher among the unemployed than in full-time employees (11.3% vs. 7.3%). Other associations are less clear—some studies find that labor jobs are more often associated with alcohol use disorders while others find associations with employment in high occupational strata. Stressful working conditions can be associated with drinking level, but employment status may also influence recovery. The 2011 NSDUH showed a higher proportion of illicit drug use disorders among the unemployed (6.1%) as compared with those employed full- or part-time (1.8% and 3.5%, respectively). Findings from the NCS indicate that high occupational strata are associated with drug use disorders.

Marital Status

Marital status has been found to be related to the occurrence of alcohol disorders and drinking behavior, but understanding the temporal relationships may be difficult. Analyses of NESARC showed that persons in stable marriages or cohabiting had the lowest 12-month prevalence of alcohol use disorders (6.1%) as opposed to adults who had never married (15.9%). Individuals who had never married also have the highest prevalence of drug use disorders. Lack of marital stability and the periods of transition to and from marriage or divorce appear to influence substance use, treatment outcomes, and drug-related mortality.

Educational Level

Studies of the relationship between educational level and drinking patterns as well as the development of alcohol use disorders may yield conflicting results. Recent analyses of the 2011 NSDUH show that binge and heavy alcohol use was lower among those who graduated from college. Moreover, studies using prospective data have shown that dropping out of high school or leaving college early is associated with an increased risk of alcohol use disorders in adulthood. Poor educational achievement and some early school behaviors are associated with risk for alcohol use disorder. These associations are bidirectional, and genetic factors may be associated with both. Lifetime prevalence of drug use disorders also varies by educational level. The proportion of those with substance use disorders is lowest for college graduates. One study found that high-risk youth had greater access to drugs as well as greater adverse consequences from drug use relative to students considered low risk.

COMORBIDITY OF ALCOHOL AND DRUG USE DISORDERS

Many clinical studies and assessments, including NCS and NESARC, document the comorbid occurrence of substance use disorders with psychopathology. The temporal order of comorbid psychiatric conditions with alcohol use disorders appears to occur bidirectionally, although alcohol use disorders are more commonly the primary condition. Alcohol use disorders are also frequently comorbid with other drug use disorders. Outcomes tend to be worse for individuals with co-occurring psychiatric and substance use disorders.

KEY POINTS

1.  A number of major surveys in the United States and internationally have assessed the prevalence of addiction. These include the Epidemiologic Catchment Area (ECA) study, the National Comorbidity Study (NCS), the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), the Monitoring the Future (MTF) study, and the annual National Survey on Drug Use and Health (NSDUH).

2.  Prevalence and incidence of alcohol use disorders and illicit drug use disorders are higher for men than for women. There is a general decline of both prevalence and incidence of alcohol and drug use disorders with age.

3.  There have not been significant changes over the past decade in terms of overall use of alcohol or illicit drugs as a whole. However, use of tobacco products has declined over the prior decade based on data from the NSDUH.

4.  There are many correlates and suspected risk factors for alcohol and drug use disorders.

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