When did NSDUH make the change from DSM-IV to DSM-5 for assessing mental health and substance use disorders?

Substance use disorder (SUD) was assessed by DSM-IV criteria in 2019 and earlier but was assessed by DSM-5 criteria for all of 2020—both quarter 1 and quarter 4. Although there were major changes to the survey over the course of that year, questions assessing SUD were the same for both quarters. This continues in 2021 and beyond. 

Measures of Major Depressive Episodes (MDEs) are based on DSM-5 and have been since 2017.

Any mental illness (AMI) and serious mental illness (SMI) are based on a model that has been calibrated to the DSM-IV since 2008, but plans are underway to change to DSM-5 within the next few years. Detailed information on past changes to mental illness estimates can be found in section 3.4.7 of the 2019 Methodological Summary and Definitions document.