Use this summary report to properly interpret 2019 NSDUH estimates of substance use and mental health issues. The report accompanies theannual detailed tablesand covers overall methodology, key definitions for measures and terms used in 2019 NSDUH reports and tables, and selected analyses of the measures and how they should be interpreted.The report is organized into five chapters:Introduction.Description of the survey, including information about the sample design, data collection procedures, and key aspects of data processing such as development of the analysis weights.Technical details on the statistical methods and measurement, such as suppression criteria for unreliable estimates, statistical testing procedures, issues around data accuracy, and measurement issues for selected substance use and mental health measures.Special topics related to prescription psychotherapeutic drugs.A comparison between NSDUH and other sources of data on substance use and mental health issues, including data sources for populations outside the NSDUH target population.An appendix covers key definitions used in NSDUH reports and tables.