Chapter 7. Discussion
The data from the 1999 and 2000 National Household Survey on Drug Abuse represent a major advance in the study of substance use and abuse in the United States. A total of nearly 138,000 Americans, including 50,000 youths aged 12 to 17, participated in the NHSDA over these two years. With this expanded sample, first implemented in 1999, the NHSDA is now a much more powerful tool for tracking trends and identifying geographic and demographic variation in patterns of use. This report, along with the supplemental data tables SAMHSA is making available simultaneously, constitutes the first release of the 2000 data. The amount of data in these tables is substantial, yet it is only a small part of what is possible from the NHSDA data files. Much of what was collected has not been tabulated, and much of what has been tabulated has not been fully analyzed. More in-depth analyses of these data will be carried out later. This report, as suggested by its title, is only intended to summarize the major findings from the 2000 NHSDA.
To summarize the results of the 2000 NHSDA, two general conclusions can be stated. First, substance use rates were generally level or declining between 1999 and 2000. Second, use and abuse of licit and illicit substances in the U.S. remains a major problem, affecting a large proportion of the population. These conclusions are supported by the following key findings from this report:
Scope of the Problem
Comparison With Monitoring the Future Study (MTF)
In the past, the NHSDA and MTF have generally shown similar long-term trends in the prevalence of substance use among youths. This has been the case despite the substantial differences in methodology between these two primary surveys of youth substance use. There were some inconsistencies in year-to-year changes, but these discrepancies could be explained by sampling errors. With the five-fold expansion in the NHSDA sample of youths, greater consistency in estimates of short-term trends between the two surveys is expected. Listed below are some key findings from the 2000 MTF data. These findings show remarkable consistency with the 2000 NHSDA results for youths aged 12 to 17:
Long-term Trends in Illicit Drug Use
The NHSDA estimates presented in this report are not strictly comparable to estimates from NHSDA surveys prior to 1999, because of the shift from paper and pencil interviewing (PAPI) to computer-assisted interviewing (CAI) in 1999 and the effect that this methodological change has on the estimates. However, it is important to discuss the 1999 and 2000 data in the context of the results from the earlier surveys.
The estimated numbers of past month illicit drug users in the U.S. in 1999 (13.8 million) and 2000 (14.0 million) are similar to estimates based on the NHSDAs conducted from 1992 through 1998. The estimate for 1992 was 12.0 million, and the estimate for 1998 was 13.6 million. The small increase that occurred during that period was primarily due to an increase in use among youths aged 12 to 17. The rate of use among youth doubled between 1992 and 1995, from 5.3 percent to 10.9 percent. After 1995, the youth rate varied from year to year and declined significantly from 1997 to 1998. Estimates from the supplemental PAPI sample employed with the 1999 NHSDA indicated a continuing decline in 1999, to 9.0 percent. This estimate is still higher than the 1992 rate. Although they are not strictly comparable to the 1995-1999 PAPI estimates, the 1999 and 2000 estimates of youth past month illicit drug use from the redesigned NHSDA (9.8 percent in 1999 and 9.7 percent in 2000) indicate little change from the rates seen during the late 1990s. These 1999 and 2000 rates are similar to the 1995 rate and are well above the 1992 rate.
Prior to the increase in youth illicit drug use in the early to mid 1990s, there had been a period of significant decline in drug use among both youth and adults. This occurred from 1979, the peak year for illicit drug use prevalence among adults and youth, until 1992. During that period, the number of illicit drug users dropped from 25 million to 12 million. The rate of use dropped from 14.1 percent of the population aged 12 and older to 5.8 percent. Among youths aged 12 to 17, the rate fell from 16.3 percent to 5.3 percent. Thus, while the rate of illicit drug use among youths in 2000 is approximately twice the rate in 1992, it is still significantly below the peak rate that occurred in 1979. Similarly, the overall number and rate of use in the population is roughly half of what it was in 1979.
Prior to 1979, the peak year for illicit drug use, there had been a steady increase in use occurring throughout the 1970s (NIDA, 1983). Although the first national survey to estimate the prevalence of illicit drug use was conducted in 1971, estimates of illicit drug initiation, based on retrospective reports of first-time use, suggest that the increase had begun in the early or mid-1960s (Gfroerer and Brodsky, 1992). These incidence estimates suggest that illicit drug use prevalence had been very low during the early 1960s, but began to increase during the mid 1960s as substantial numbers of young people initiated the use of marijuana. As discussed in Chapter 5 of this report, annual marijuana incidence increased from about 553,000 new users in 1965 until it reached a peak of 3.2 million initiates per year in 1976 and 1977, 2 to 3 years before the prevalence rates peaked. Interestingly, the annual number of marijuana initiates reached a low point in 1990 (1.4 million), then increased, two years before the increase in youth prevalence occurred. This demonstrates the value of the incidence data in forecasting future trends in prevalence. Assuming this relationship between incidence and prevalence continues to hold, the significant decline in marijuana incidence between 1998 and 1999 indicates that a decline in youth prevalence is occurring or will soon occur. However, the long-term impact of the elevated marijuana initiation rates during the mid to late 1990s (2.5 million new users per year, on average, during 1995 to 1998) is likely to be an increase in the number of people needing treatment for substance abuse problems, as the cohort of 1990s initiates ages along with the cohort of baby boomers that had elevated marijuana initiation levels during the 1970s.
Limitations of the Data
The expansion and redesign of the NHSDA resulted in greater analytic potential and improved precision of prevalence estimates generated from the NHSDA. However, there are still important limitations with the NHSDA data that NHSDA data users must be aware of. This report contains several appendices that describe the NHSDA methodology and the limitations of these data. Readers are encouraged to take advantage of these appendices when using these data. SAMHSA will also be providing more detailed information on the NHSDA methods in reports that will be available on the SAMHSA website.
Appendices E and F in this report include a number of tables showing various estimates from the 1999 and 2000 NHSDAs. These tables are a small subset of all the tables that have been produced at this time. The full set of tables, referred to as the Summary Tables from the 2000 NHSDA, can be accessed at SAMHSA's website. The Summary Tables are organized into these major categories: Illicit Drug Use, Tobacco and Alcohol Use, Risk and Protective Factors, Incidence, Miscellaneous, and Sample Size and Population. These detailed Summary Tables include estimates of standard errors for all prevalence estimates shown.
This page was last updated on June 03, 2008.