In 2010, an estimated 20% of adults aged 18 years and older in the United States – almost 46 million adults – had experienced "any mental illness" in the past year, with those aged 18-25 years, women, and the unemployed among the groups most affected, according to a report issued Jan. 19 by the Substance Abuse and Mental Health Services Administration (SAMHSA).

A "relatively high" prevalence rate of mental illness during the previous year, a strong association between mental illness during the previous year and substance abuse, as well as a "substantial unmet need" for mental health care during the previous year are among the key findings, the report concluded.

The report also found that that 8% of adolescents aged 12-17 years (almost 2 million individuals) had experienced a major depressive episode in the past year, and that illicit drug use was more than twofold greater among these adolescents than among those who had not used illicit drugs (37% vs. 18%). In addition, 12% of people in this age group (almost 3 million individuals) had received treatment or counseling for emotional or behavioral problems in an inpatient or outpatient mental health setting. "Feeling depressed" was the most common reason for using these services, in almost 50% of cases, the report said.

The SAMHSA report defined "any mental illness" as having had, at the current time or at any time during the past year, "a diagnosable mental, behavioral, or emotional disorder (excluding developmental and substance use disorders) of sufficient duration to meet diagnostic criteria" specified in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), regardless of functional impairment. The 20% figure in adults was similar to the rate of the previous year. Nearly 30% of the adults aged 18-25 years and 22% of those aged 26-49 years had had a mental illness in the past year, compared with 14% of those aged 50 years and older. Unemployed people were also more likely to have had a mental illness in the past year (28%), compared with people who worked full time (17%) or part time (23%).

The rate of "serious mental illness" – which was defined the same way as "any mental illness," but one that was "of sufficient duration" to meet diagnostic DSM-IV criteria and had "resulted in serious functional impairment, which substantially interferes with or limits one or more major life activities" – followed a similar pattern.

An estimated 5% of adults aged 18 years and older (about 11.4 million adults) had had a serious mental illness, similar to the rate of the previous year. The rate of serious mental illness was highest among those aged 18-25 years (8%), followed by those aged 26-49 years (6%), compared with 3% of those aged 50 years and older. Almost 8% of unemployed adults had a serious illness, compared with 4% of those who were employed full time and 6% of those who were employed part time.

Women were more likely to be affected than men by any mental illness (23% vs. 17%) and serious mental illness (7% vs. 3%).