1998 National Household Survey on Drug Abuse

12. DISCUSSION OF RESULTS

The 1998 National Household Survey on Drug Abuse provides a comprehensive description of substance use and abuse in the United States. The survey provides reliable information to assess trends, patterns, and relationships associated with substance abuse. Given the difficulties involved in collecting data on illegal and sensitive behaviors, the interpretation of the NHSDA data is best made in conjunction with other available data sources, taking into account the strengths and limitations of each source.

The 1998 NHSDA data show that overall drug use remained level, and the rate of drug use among youths fluctuated and may have also leveled off or possibly started to decrease after a period of increase from 1992 to 1995. Nevertheless, estimated rates of youth initiation of marijuana and heroin use remained at historically high levels.

Comparisons of the NHSDA results for youth marijuana use with results from other surveys show that the trends during the 1990s are generally consistent across these surveys. The NHSDA showed substantial increases in past month use among youths age 12-17 from 1992 to 1995 (from 3.4 percent to 8.2 percent), then rates of 7.1 percent in 1996, 9.4 percent in 1997, and 8.3 percent in 1998 . The Monitoring the Future (MTF) study showed that past month marijuana use among high school seniors increased from 11.9 percent in 1992 to 21.2 percent in 1995. The rate did not change significantly in 1996 (21.9 percent), 1997 (23.7 percent) and 1998 (22.8 percent). The Partnership Attitude Tracking Study (PATS), a nationally representative survey of students sponsored by the Partnership for a Drug-Free America, estimated rates of past month marijuana use for students in grades 7-12 to be 14 percent in 1993, 21 percent in 1995, 22 percent in 1996, 24 percent in 1997, and 23 percent in 1998 (PDFA 1999).

The NHSDA data on youth drug use are not, however, entirely consistent with the MTF and PATS data when specific year to year variations and trends among subgroups of youth are examined. Further analysis of these data may help explain these differences, but it is also important to recognize the methodological differences between the NHSDA and the MTF and PATS that could be the cause. Differences in populations covered, time periods of data collection, questionnaire wording, effects of nonresponse bias, and interview setting (school vs, home) could affect the resulting estimates, both in terms of levels and trends (Gfroerer, Wright, and Kopstein 1997).

The estimated annual number of new marijuana users increased from 1.4 million in 1991 to 2.4 million in 1994, and remained at about the same level in 1995, 1996 and 1997. During 1995-1997, the rate of marijuana initiation among youths age 12-17 was at its highest level ever. This has important implications for substance abuse prevention and treatment efforts. In terms of prevention, there is an obvious need to focus immediate attention on children and adolescents. In the long run, the expanding pool of young people using illicit drugs will probably result in continuing pressure on the substance abuse treatment system in future years, as many new drug users progress to addiction and require intervention. Data from SAMHSA's Treatment Episode Data Set (TEDS), which collects data from publicly funded substance abuse treatment programs, have shown large increases in the number of admissions for a marijuana problem, from 91,000 in 1992 to 192,000 in 1997, with the greatest rate of increase occurring in the 12-17 age group. A recent analysis showed that if current initiation rates continue, the size of the population needingtreatment for a drug abuse problem is estimated to grow by 57 percent by the year 2020 (Gfroerer and Epstein 1999).

Reports of increasing heroin and methamphetamine abuse have been prominent over the past few years, based on data from medical examiners, emergency departments, and drug treatment facilities (NIDA 1999; SAMHSA 1998b). The limitations of the NHSDA for measuring rare and stigmatized drug use behaviors have made it difficult to either refute or support these reports.

The NHSDA data showed an increasing rate of past month heroin use from 1993 to 1997, and an increasing rate of lifetime heroin smoking, snorting, or sniffing between 1994 and 1997. The shift toward non-injection heroin use has also been observed in TEDS data. In 1992, 77 percent of heroin users entering publicly funded treatment programs were injectors and in 1997 68 percent were injectors. The 1998 NHSDA data suggest a reduction in heroin use. Past year use declined from 597,000 users in 1997 to 253,000 in 1998, a statistically significant change. However, the change from 325,000 past month users in 1997 to 130,000 past month users in 1998 was not statistically significant. The decrease in 1998 was significant in the 35 and older age group for past month use. Rates of heroin initiation increased for both youths age 12-17 and for young adults age 18-25 between 1990 and 1996, but did not change between 1996 and 1997. The average age of new heroin users, which ranged from 23 to 27 during 1988-1992, was down to 17.9 years in 1997. Most new heroin users in recent years were under age 26 and were smoking, snorting, or sniffing heroin.

Methamphetamine use (lifetime) rates also suggest some increase, although the change between 1994 and 1997 was not statistically significant. There was a statistically significant increase in lifetime methamphetamine use among youths age 12-17 from 1996 to 1997, but a significant decrease from 1997 to 1998. Other data sources have indicated a substantial increase in methamphetamine use during the 1990s. For example, there has been an increase in methamphetamine admissions to publicly-funded treatment programs (from 14,000 in 1992 to 53,000 in 1997).

The NHSDA continues to show the aging of the drug using population. Cohorts who were teenagers and young adults in the 1960s and 1970s are now older, and although most no longer use illicit drugs, many still do. This aging cohort, composed primarily of the baby boom, is adding increasingly to the "35 and older" age group shown in NHSDA reports. Thus, the proportion of drug users that are age 35 and older continues to increase (from 10 percent of users in 1979 to 32 percent of users in 1998). Data from the Drug Abuse Warning Network (DAWN) on drug-related hospital emergency department episodes also show the impact of the aging cohort of drug users. In 1979, 12 percent of patients with cocaine episodes were age 35 or older. By 1985 the proportion was 19 percent, and by 1997 it was 46 percent.

Many of the drug users in this aging cohort have used drugs for many years and have developed severe drug problems. These aging drug abusers are expected to place a continuing demand on the drug abuse treatment system. Projections indicate that the number of people age 50 and older needing treatment for a drug problem will increase fivefold in the next 20 years (Gfroerer and Epstein 1999). This aging cohort of heavy drug users is also a factor in the continuing rise in hospital emergency department episodes, which are more likely to involve these heavy users than occasional users or those who use only marijuana. Cocaine-related emergencyroom visits have increased from 5,000 in 1981 to 29,000 in 1985 (the peak year for past month cocaine prevalence in the NHSDA) to 161,000 in 1997. Heroin-related emergency room visits have increased from 12,000 in 1979 to 72,000 in 1997 (SAMHSA 1996c, 1999a).

It is important to recognize the limitations of both DAWN and the NHSDA for measuring the prevalence of heavy drug use. As is discussed in DAWN reports, there are many factors that could influence trends in drug-related episodes. These factors include changes in the purity and availability of drugs, changes in patterns of use (e.g., drug combinations or route of administration), availability of treatment programs ("seeking detoxification" was the reported reason for visit in 25 percent of cocaine-related episodes in 1995), and changes in patient management practices. Furthermore, research has indicated that only a small, nonrepresentative proportion of heavy cocaine users account for cocaine-related emergency room episodes (Gfroerer and Brodsky 1993).

Sample size, coverage, and validity problems are likely to be more pronounced for NHSDA estimates of heavy users than for other measures generated by the survey. Therefore, estimates of heavy use are considered conservative, and changes over time are generally not statistically significant. For example, the NHSDA has produced estimates of about 600,000 frequent cocaine users with no significant changes in the size of this population since 1985. By using various other data sources and making a number of assumptions (many of which are of uncertain validity), researchers have estimated that there are over 2 million frequent cocaine users in the U.S. (ONDCP 1998).

Clearly there is considerable uncertainty about the size of the heavy drug-using population. Estimates from the NHSDA can provide useful data to help describe this population, but should only be used in conjunction with other data sources. Appendix 2, Section V (Estimation of Heavy Drug Use) contains a discussion of a methodology developed by OAS that uses arrest and treatment data to adjust NHSDA estimates of heavy drug use.