"Inhalants rank second among the illicit drugs in lifetime prevalence for 8th graders (9.5%) and third for 10th graders (6.8%); but they rank eighth for 12th graders (5.3%). Inhalants also rank second-highest in 30-day prevalence among the illicit drugs for 8th graders (2.1%) and fourth (1.1%) among 10th graders, but they rank lower for 12th graders (0.9%). Note that the youngest respondents report the highest levels of use; this is the only class of drugs for which current use declines with age during adolescence.3"
3: "The results also indicate declining lifetime inhalant prevalence at higher grades, which could be due to various factors. There might be lower lifetime prevalence at older ages because the eventual school dropout segment is included only in the lower grades. If those who will become dropouts are unusually likely to use inhalants, lifetime use rates could decline with grade level. That would lead to a relatively stable difference between the grades in lifetime use (because dropout rates have been fairly stable in recent years); however, the degree of difference has changed some over time, with larger differences emerging in the mid-1990s. Another possible factor is changing validity of reporting with age; but in order to account for the trend data, one would have to hypothesize that this tendency became stronger in the 1990s, and we have no reason to believe that it did. Cohort differences may be a factor, but cannot completely explain the large changes in lifetime prevalence. It seems likely that all of these factors contribute to the differences observed in the retrospective reporting by different ages, and possibly some additional factors as well."
Miech, R. A., Johnston, L. D., O’Malley, P. M., Bachman, J. G., Schulenberg, J. E., & Patrick, M. E. (2020). Monitoring the Future national survey results on drug use, 1975–2019: Volume I, Secondary school students. Ann Arbor: Institute for Social Research, The University of Michigan.