https://doi.org/10.1177/1087054719855689 Journal of Attention Disorders 1–12 © The Author(s) 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1087054719855689 journals.sagepub.com/home/jad Article The prevalence of attention deficit hyperactivity disorder (ADHD) among adults is a function of children and adoles- cents who have been diagnosed with ADHD aging into adulthood, diagnoses that have occurred during adulthood, and mortality. As such, the point prevalence of ADHD in the adult population, especially at younger ages when mor- tality is less of a concern, is largely shaped by changes in historical context and policy that differentially shape the experiences of cohorts and historical period effects that have broad effects across all age groups. In part, due to data limitations, no national, population- representative study has been able to examine inter- and intra-cohort changes in ADHD among adults. To a substan- tial degree, inter-cohort variation reflects changes in diag- nostic criteria, lay referral, and professional practice that affected children and adolescents as they came of age dur- ing different historical time periods. Using repeated cross- sectional data from two or more points in time, adults born and raised in different historical periods can be compared at the same age to reveal the extent of inter-cohort change. Intra-cohort variation among adults primarily reflects change in the propensity to diagnose during a particular his- torical period. Such an effect has the potential to impact all age groups, although subpopulations may be differentially impacted. Using repeated cross-sectional data from two or more points in time, synthetic cohorts can be constructed to estimate change as cohorts age. In this article, we use data from the 2007 and 2012 U.S. National Health Interview Survey (NHIS) to document inter- and intra-cohort changes in adult ADHD and examine whether these vary by gender. Our study is limited to these two cross-sectional surveys because they are the only years that the NHIS asked adults whether they had ever been diagnosed with ADHD. Historical Context The history of the medicalization of childhood deviance, including excessive hyperactivity, inattentiveness, and impulsivity, and the evolution of the diagnostic criteria for the psychiatric condition that encompasses those behaviors, are both well-documented (Conrad & Schneider, 1980/2010; Conrad, 2008; Lange, Reichl, Lange, Tucha, & Tucha, 2010). The development of the contemporary diagnosis “ADHD” can be traced back as far as 1798, from the initial description in the medical literature of similar symptoms in children to the more recent establishment and repeated 855689JAD XX X 10.1177/1087054719855689Journal of Attention DisordersLondon and Landes research-article 2019 1 Syracuse University, NY, USA Corresponding Author: Andrew S. London, Associate Dean and Professor of Sociology, Maxwell School of Citizenship and Public Affairs, Syracuse University, Maxwell Dean’s Office, 200 Eggers Hall, Syracuse, NY 13244, USA. Email: anlondon@maxwell.syr.edu Cohort Change in the Prevalence of ADHD Among U.S. Adults: Evidence of a Gender-Specific Historical Period Effect Andrew S. London 1 and Scott D. Landes 1 Abstract Objective: To document inter- and intra-cohort changes in adult ADHD and examine whether changes vary by gender. Method: We analyze data from the 2007 and 2012 U.S. National Health Interview Survey. Results: The prevalence of ADHD among adults aged 18 to 64 years increased from 3.41% in 2007 to 4.25% in 2012. As expected, patterns of inter- and intra-cohort change varied by gender. At younger ages, inter-cohort gender differences are more distinct due to a spike in prevalence among boys/men born in or after 1980. Consistent with a gender-specific historical period effect, recent intra-cohort increases among women have narrowed the gender gap. Conclusion: The gender gap in the prevalence of ADHD among adults decreased by 31.1% from 2007 to 2012 due to increased prevalence among adult women of all ages. We discuss these results in relation to diagnostic practice, adult health and well-being, data limitations and needs, and directions for future research. (J. of Att. Dis. XXXX; XX(X) XX-XX) Keywords ADHD, adult health, gender, prevalence, cohort change, historical period effect