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11. DISCUSSION OF RESULTS

The 1995 National Household Survey on Drug Abuse provides a comprehensive description of substance use and abuse in the United States. Despite its limitations, the NHSDA provides reliable information to assess trends, patterns, and relationships associated with substance abuse. The interpretation of the NHSDA data is best made when studied in conjunction with other available data sources, taking into account the strengths and limitations of each source.

The 1995 NHSDA data clearly show a continuing increase in illicit drug use prevalence among youths. The increase in marijuana use seen in the 1994 NHSDA has continued in 1995. In addition, increases in hallucinogen and cocaine use among youth were found in the 1995 NHSDA. The NHSDA results are consistent with the results of the Monitoring the Future (MTF) Study, which has shown statistically significant increases in drug use among eighth, tenth, and twelfth graders from 1992 through 1995 (USDHHS, 1995). Despite methodological differences (e.g., populations covered and data collection methods) between MTF and NHSDA that affect the levels of drug use prevalence reported, both surveys show recent increases in the use of marijuana, cocaine, and hallucinogens among adolescents. The MTF and the 1994 NHSDA both show that perceived risk of harm in using drugs, a key correlate of drug use, has decreased among youths in recent years, and that drugs are easily accessible to young people.

Newly developed estimates of trends in drug use incidence (i.e., initiation) provide a different measure of the drug use situation. They can provide an early indication of emerging patterns of use. The estimated annual number of new marijuana users increased from 1.4 million in 1991 to 2.3 million in 1994, indicating no signs of any reversal of the upward trends in prevalence.

The recent upturn in illicit drug use among youths 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 increasing proportion 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.

Reports of increasing heroin and methamphetamine use have been prominent over the past few years, based on data from medical examiners, emergency departments, and drug treatment facilities (NIDA 1996a; Greenblatt, Gfroerer and Melnick 1995). The limitations of the NHSDA for measuring these kinds of drug use behaviors have made it difficult to either refute or support these reports. However, the 1995 NHSDA data show an increasing rate of heroin smoking (in lifetime) between 1994 and 1995, particularly among adults age 35 and older. Methamphetamine use (lifetime) rates also suggest some increase, although the change between 1994 and 1995 was not statistically significant.

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 27 percent of users in 1995). 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 and older. By 1985 the proportion was 19, and by 1995 it was 43.

Many of the drug users in this aging cohort have used drugs for many years and have developed severe drug problems. This may partly explain 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 emergency room 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 142,000 in 1995. Heroin-related emergency room visits have increased from 12,000 in 1979 to 76,000 in 1995 (SAMHSA 1996d,e).

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. (Rhodes 1993).

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 contains a discussion of a methodology developed by OAS that uses arrest and treatment data to adjust NHSDA estimates of heavy drug use.

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