One in 5 American adults aged 18 or older, or 45.6 million people, had mental illness in the past year, according to a report from the Substance Abuse and Mental Health Services Administration (SAMHSA).

The 2011 National Survey on Drug Use and Health (NSDUH): Mental Health Findings report presents results pertaining to mental health from the 2011 NSDUH, the primary source of statistical information on the use of illegal drugs, alcohol, and tobacco by the civilian, noninstitutionalized population of the United States aged 12 years or older. Conducted by the federal government since 1971, the survey collects data through face-to-face interviews with approximately 65,750 people aged 12 years or older nationwide, at the respondent's place of residence.

The rate of mental illness was more than twice as high among those aged 18 to 25 (29.8 percent) than among those aged 50 and older (14.3 percent), the report said. Adult women also were more likely than men to have had mental illness in the past year (23.0 percent versus 15.9 percent), it said.

Mental illness among adults aged 18 or older is defined as having had a diagnosable mental, behavioral, or emotional disorder (excluding developmental and substance use disorders) in the past year, based on criteria specified in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association.

The 2011 NSDUH also shows that 11.5 million adults (5 percent of the adult population) had serious mental illness in the past year. Serious mental illness is defined as mental illness that resulted in serious functional impairment, which substantially interfered with or limited one or more major life activities.

The rates of mental illness remained stable between 2010 and 2011.

"Although mental illness remains a serious public health issue, increasingly we know that people who experience it can be successfully treated and can live full, productive lives," said SAMHSA Administrator Pamela S. Hyde. "Like other medical conditions, such as cardiovascular disease or diabetes, the key to recovery is identifying the problem and taking active measures to treat it as soon as possible."

The report says that among adults with mental illness in the past year, about 4 in 10 adults (38.2 percent of adults with mental illness) received mental health services during that period. Among those who had serious mental illness in the past year the rate of treatment was notably higher (59.6 percent).

The report also notes that an estimated 8.5 million American adults (3.7 percent) had serious thoughts of suicide in the past year -- among them 2.4 million (1.0 percent) made suicide plans and 1.1 million (0.5 percent) attempted suicide. Those in crisis or knowing someone they believe may be at immediate risk of attempting suicide are urged to call the National Suicide Prevention Lifeline 1-800-273-TALK (8255) or go to http:/www.suicidepreventionlifeline.org. The Suicide Prevention Lifeline network, funded by SAMHSA, provides immediate free and confidential crisis round-the-clock counseling to anyone in need throughout the country, everyday of the year.

According to the report, rates for substance dependence or abuse were far higher for those who had mental illness than for the adult population which did not have mental illness in the past year. Adults who had mental illness in the past year were more than three times as likely to have met the criteria for substance dependence or abuse in that period than those who had not experienced mental illness in the past year (17.5 percent versus 5.8 percent). Those who had serious mental illness in the past year were even more likely to have had substance dependence or abuse (22.6 percent).

The report also has important findings regarding mental health issues among those aged 12 to 17. According to the report 2.0 million youth aged 12 to 17 (8.2 percent of this population) had experienced a major depressive episode in the past year. A major depressive episode is defined as a period of at least two weeks when a person experienced a depressed mood or loss of interest or pleasure in daily activities and had at least four of seven additional symptoms reflecting the criteria as described in the Diagnostic and Statistical Manual of Mental Disorders.

In addition, the report finds that young people aged 12 to 17 who experienced a major depressive episode in the past year have more than twice the rate of past year illicit drug use (36.0 percent) as their counterparts who had not experienced a major depressive episode during that period (17.4 percent).

The complete survey findings from this report are available on the SAMHSA Web site at http://www.samhsa.gov/data/NSDUH/2k11MH_FindingsandDetTables/index.aspx.