The Epidemiology of Adolescent Inhalant Drug Involvement FREE

THE ESTIMATED risk of starting to use inhalant drugs has increased 3-fold among 12- to 17-year-olds in the United States during the past decade—from 7.2 cases per 1000 person-years in 1983 to 21.5 cases per 1000 person-years in 1993.¹ Results of 2 continuing national surveys on the illicit drug use of school-aged students (the Monitoring the Future Study and the American Drug and Alcohol Survey) indicate that in the 1990s, marijuana and inhalant drugs vie with one another as the first and second most commonly used illicit drugs in this age group.^2- 4 Along with the high incidence and prevalence of inhalant use, the age at which these drugs are first being used seems to be decreasing with time.³ Despite these trends, there is a relative paucity of information about the epidemiological determinants and natural history of inhalant drug involvement among adolescents in this country.^5- 7

In the present report we try to fill some gaps in our knowledge of inhalant use by examining variations in the occurrence of inhalant use in a nationally representative sample of adolescents surveyed between 1990 and 1995. Specifically, we examine patterns of initiation of inhalant use among 12- to 17-year-olds, sex and race or ethnicity differences in the use of these drugs, and the prevalence of use of specific inhalants over time. In addition, we examine the extent to which inhalant use is no more than a transitory behavior in this young population.

Although some reports described the patterns of inhalant use across different sociodemographic characteristics, none relied on nationally representative community samples. The present study is the first to draw on samples selected to reflect the noninstitutionalized civilian population of the United States. These samples were drawn, recruited, and assessed in a fashion that allows the study of variations from year to year with a minimum of methodological sources of variability. In contrast to school surveys such as Monitoring the Future Study, this study's data are from representative samples of all school-aged youths living in households, including dropouts.

The data analyzed for this report were from public domain files of data collected as part of the National Household Survey on Drug Abuse (NHSDA). The annual NHSDA is designed to provide cross-sectional information about the patterns of drug use among household residents of the United States aged 12 years and older at the time of contact. Details of the sampling and interview methods have been described extensively elsewhere.^8- 13 Each year between 1990 and 1995, multistage probability sampling methods have been used to draw nationally representative samples ranging from 9259 to 32594 in size. Household screening completion rates ranged from 94% to 96%, and interview response rates ranged from 77% to 84% across survey years. Certain age and race or ethnic groups were oversampled to ensure more stable estimates of drug use in these population subgroups. The sample selected for the present report includes the 34826 adolescents aged 12 to 17 years who participated in the NHSDA from 1990 to 1995 (Table 1).

The NHSDA questionnaire is a standardized and structured interview schedule administered by trained lay interviewers in a private location after assurances of confidentiality and after obtaining informed consent. Participation of persons younger than 18 years depends on consent of the individual and a parent or guardian, unless parental consent is not obtainable (eg, youths in college, dormitories, or shelters for runaways or abused children). Parents are permitted to inspect the questionnaire before administration. Furthermore, the interviewer explains to the parent and youth that no one, including the parent, will be allowed to see the youth's completed questionnaire. Also, the youths are shown a federal confidentiality certificate indicating that federal law requires all information obtained to be used for research purposes only. Self-administered answer sheets are used to minimize underreporting of potentially sensitive information such as illicit drug use.

For this report, a lifetime history of inhalant use was defined as ever having sniffed or inhaled 1 or more of the following substances "for kicks or to get high": gasoline or lighter fluid; butane, propane, or other light gases; spray paints or other aerosol sprays; glue (eg, shoeshine liquid, glue, toluene); solvents (eg, lacquer thinner or other paint solvents); amyl nitrite; ether or other anesthetics; nitrous oxide; and cleaning fluids. Respondents were classified as having recently "initiated" inhalant use if they reported that their first use of any of these substances occurred within the year before the interview. Specifically, incident cases of inhalant use were persons who reported age of first use as equal to age at interview or age at interview minus 1. It follows that the incidence of inhalant use was defined as the number of new cases (incident cases) divided by the number of respondents who never used inhalants plus new cases.

Prevalence proportions and incidence rates of inhalant use were estimated based on weighted data to account for the NHSDA's differential sampling probability design. Taylor series linearization (using statistical analysis software [SUDAAN, Research Triangle Institute, Research Triangle Park, NC]) was used to account for the design effects of the multistage sampling process in the estimation of variances.¹⁴

Differences in rates of inhalant use across racial groups were examined using a poststratification strategy in conjunction with the conditional form of multiple logistic regression.¹⁵ This approach involves grouping respondents into risk sets based on neighborhood of residence. Poststratification with conditional logistic regression controls for the possible confounding effects of unmeasured but commonly shared community-level characteristics (eg, drug availability, police presence, and social disadvantage shared across the neighborhood). The models also included adjustment for the suspected distorting effects of sex and age. Hence, in the reported analyses on race and ethnicity in association with inhalant use, we are holding constant shared neighborhood characteristics and possible age and sex differences between users and nonusers who live in the same neighborhoods. Estimated odds ratios were derived from the antilog of the regression coefficient estimates; the 95% confidence intervals are based on SEs derived from the logistic models using statistical analysis software (EGRET, Statistics and Epidemiology Research Corp, Seattle, Wash).¹⁶

The risk of initiating inhalant use is not limited to early adolescence. As shown in Table 2, year by year, the estimated rate of starting inhalant use for 17-year-olds was as great or greater than the estimated rate for 12-year-olds. Overall, from 1990 through 1995, the largest incidence estimates are seen for 14- and 15-year-olds (Table 2).

A comparison of male-female inhalant use shows that in 1990 boys were nearly twice as likely as girls to report ever having used inhalants (9.6% vs 5.8%, P=.03). In the subsequent years there were no significant or consistent male-female differences in the lifetime prevalence of inhalant drug use (Figure 1). For 1990 through 1995 overall, the lifetime prevalence estimates for girls and boys were virtually identical (6.6% vs 6.9%).

Table 3 and Figure 2 depict the trends of inhalant use for adolescents of 4 racial or ethnic categories. The lifetime history of inhalant use was highest among non-Hispanic whites and lowest among non-Hispanic blacks in 4 of the 6 years studied. Inhalant use among non-Hispanic whites decreased from 1990 to 1992 and then steadily increased. By 1995, the lifetime history estimates among non-Hispanic whites had returned to the 1990 proportion of almost 9%. On the other hand, non-Hispanic black youths experienced a steady decline in lifetime history of inhalant use until 1993 (from ≥6% to <2%), at which point the percent leveled off. The estimated lifetime prevalence of inhalant use among Hispanic youths was lower than that of non-Hispanic whites in 1990, 1991, 1994, and 1995 and was only slightly higher in 1992 and 1993. Estimates of lifetime history of inhalant use among members of the "other" race category are based on small numbers of inhalant users and therefore are statistically unreliable.

Conditional logistic regression analysis was used to compensate for possible effects of community-level characteristics, sex, and age on the association between inhalant use and race or ethnicity. These analyses enable a comparison of the odds of inhalant use for non-Hispanic blacks, Hispanics, and members of "other" racial categories to non-Hispanic whites, holding constant the potential confounding effects of unmeasured neighborhood characteristics.

Results from this analysis reveal that the occurrence of inhalant use was lower among non-Hispanic black adolescent respondents than among non-Hispanic white adolescents after controlling for neighborhood characteristics. Table 4 shows this difference to be statistically significant (P<.05) in the 3 years for which the sample size was largest (1991–1993); the P values approached conventional levels of significance in 1995 (P=.05). Differences between non-Hispanic white adolescents and Hispanic adolescents were not statistically significant for any of the years (P>.05).

To examine drug-specific time trends, we compared the lifetime prevalence of using specific classes of inhalant drugs in 1990 and 1995. For this analysis, the sample was restricted to respondents aged 12 to 16 years to ensure that there was no overlap of birth cohorts in the samples from these 2 years. As seen in Figure 3, there was an increase in the lifetime prevalence of inhalant use between 1990 and 1995 for all 6 inhalant drug categories shown. This trend was statistically significant for aerosols and glue (P<.05). Too few respondents reported having used the other classes of inhalants to allow for stable estimates and detection of differences.

A final set of analyses addresses the degree to which inhalant use is a transitory behavior among these adolescents. Three measures of nontransitory use were assessed: the percentage of inhalant users who reported use of multiple inhalant drugs, the percentage who reported multiple occasions of use, and the time since first inhalant use among current users. Use of more than 1 inhalant drug was reported by 31% to 49% of inhalant users from 1990 through 1995 (Figure 4). No clear time trend was evident, although the 2 highest estimates for multiple drug use were reported in the last 2 survey years. Overall, use of multiple inhalant drugs was reported by 43% of inhalant users in the 1990 through 1995 surveys.

Regarding multiple occasions of use, more than half (53%) of respondents aged 12 to 17 years reported having used inhalant drugs on more than 2 occasions, and about 16% had used inhalant drugs on more than 10 occasions (Figure 5). Finally, among respondents who reported having used inhalant drugs within the year before the interview, most (77%) had started inhalant use more than 1 year previously, about 47% had used inhalant drugs for the first time more than 2 years previously, and 10% started inhalant drug use at least 6 years before the date of the survey assessment (Figure 6).

The use of inhalant drugs, particularly aerosols and glue, increased during the first half of the present decade. The incidence estimates from this study show that inhalant use is not restricted to early adolescent boys and that inhalant use is not a transitory behavior among adolescents in the United States. A large proportion of those who use inhalants reported having taken multiple inhalant drugs and having done so repeatedly for long periods.

Overall, the highest prevalence of inhalant use occurs among non-Hispanic whites. Hispanic youths have the second highest prevalence of inhalant use, only a few percentage points below estimates for non-Hispanic whites. The groups least likely to use inhalant drugs are non-Hispanic blacks and "others." These findings generally are consistent with the results of other large-scale surveys, such as the Monitoring the Future Study and the American Drug and Alcohol Survey.¹⁷ However, results from those surveys show a greater percentage of inhalant users for each ethnic group than did the NHSDA surveys. The discrepancy in the proportion of inhalant users between the Monitoring the Future Study and the NHSDA has been addressed previously and has been attributed to several methodological differences in the 2 surveys.¹⁷

Several limitations of the present study warrant attention. First, self-reports of drug use data, as gathered in the NHSDA, lend themselves to socially desirable responding. Nonetheless, extensive measures are implemented in the design of the NHSDA to maintain accurate reporting of even sensitive information.^18- 19 Second, despite the large sample size, the NHSDA still does not yield large numbers of individuals with recent inhalant drug involvement. This raises concern about statistical precision and power. For most of the estimates, we obtained wide confidence intervals that suggest low precision and thwart in-depth analyses. In turn, the wide margin of errors observed for some of the estimates might explain some of the variability in inhalant use across the various age and racial groups. Furthermore, the small sample sizes decrease the power with which to detect differences (if present) in prevalence of inhalant use across racial or ethnic categories, preventing us from discerning age and racial patterns of use. Third, the NHSDA surveys provide annual cross-sectional estimates of patterns of drug use in the United States. Our ability to examine factors associated with inhalant drug use is limited to those "fixed" factors that remain unaffected by the onset of drug use (eg, sex, race, and age). Optimal epidemiological surveillance might involve regular tracking of cohorts as their members pass through varying ages of risk to assess temporal sequencing of events related to the use of inhalants and other drugs, such as can be done with longitudinal analyses of data from the University of Michigan's Monitoring the Future panel.³

Despite these limitations, this article provides evidence of public health significance by helping to fill gaps of information regarding the distribution of inhalant drug involvement across categories of person, place, and time. The use of inhalant drugs often is viewed as a transient behavior, a view not supported by the present findings from the NHSDA. Moreover, the behavior is a potentially dangerous one.^20- 21 Statistics from the United Kingdom indicate that approximately 5% of teenage deaths are a result of "volatile substance abuse," with up to one third of these deaths occurring among individuals using inhalants for the first time.^22- 23 Numerous reports suggest that early use of inhalants increases the likelihood of progression to more severe drug-taking behaviors or other problem behaviors.^24- 28 However, the mechanisms by which a transition between inhalant use and other drug use might take place remain unknown. The cross-sectional nature of the NHSDA data does not allow us to examine progression, and it remains an area for future investigations.

In addition to the risks of sudden death and of making a transition to other drugs, the use of inhalants poses an additional array of health hazards.^29- 31 For example, toluene abuse has been found to result in cerebellar dysfunction, and the abuse of solvents, aerosols, and adhesives has been putatively associated with renal failure, arrhythmia, and brain lesions. Despite these risks, only approximately 40% of high school students view experimentation with inhalant drugs as dangerous.³ In light of the prevalent use of inhalant drugs, their widespread availability, and the risks involved with their use, more focused attention needs to be devoted to what some have called "The Silent Epidemic."³² We hope that this report will stimulate a closer look at inhalant use by youths and will prompt future theory-testing investigations of the patterns of inhalant drug involvement in the United States and abroad.

Accepted for publication March 20, 1998.

This research was supported by training grant T32-DA07292 and research grant DA09592 from the National Institute on Drug Abuse, Rockville, Md.

Presented as a poster at the 59th annual scientific meeting of the College on Problems of Drug Dependence, Nashville, Tenn, June 17, 1997.

Editor's Note: What happened to the good old days when people enjoyed taking deep breaths of nature's own fresh air? Maybe all the pollutants in the air have numbed our senses.—Catherine D. DeAngelis, MD

Corresponding author: James C. Anthony, PhD, Department of Mental Hygiene, School of Hygiene and Public Health, The Johns Hopkins University, Hampton House 893, 624 N Broadway, Baltimore, MD 21205-1999 (e-mail: janthony@jhu.edu).