Serious mental illness (SMI) is defined as someone over the age of 18 who has (or had within the past year) a diagnosable mental, behavior, or emotional disorder that causes serious functional impairment that substantially interferes with or limits one or more major life activities. The three diagnoses most commonly associated with SMI are:
According to the 2019 National Survey on Drug Use and Health, in 2019 an estimated 13.1 million adults had SMI in the past year. This corresponds to 5.2 percent of adults.
Here is a breakdown of SMI in specific age groups:
Substance Abuse and Mental Health Services Administration. (2020). Key substance use and mental health indicators in the United States: Results from the 2019 National Survey on Drug Use and Health (HHS Publication No. PEP20-07-01-001, NSDUH Series H-55). Rockville, MD: Center for Behavioral Health Statistics and Quality, Substance Abuse and Mental Health Services Administration.