THURSDAY, Nov. 18 (HealthDay News) -- A new survey finds that 20 percent of U.S. adults -- over 45 million people -- experienced mental illness in the past year.

Overall, 4.8 percent (11 million people) suffered serious mental illness, 8.4 million people had serious thoughts of suicide, 2.2 million made suicide plans, and one million attempted suicide, according to the 2009 National Survey on Drug Use and Health.

Nearly 20 percent (8.9 million) of adults with mental illness in the past year also had a substance abuse disorder, the report found. The rate was 25.7 percent for those with a serious mental illness -- about four times higher than the rate of 6.5 percent among people without a serious mental illness.

The survey, which included 67,500 adults nationwide, was released Thursday by the Substance Abuse and Mental Health Services Administration.

Among its other findings:

Mental illness is more common among jobless people (27.7 percent) than among those with full-time jobs (17.1 percent).

Women are more likely than men to experience mental illness -- 23.8 percent vs. 15.6 percent.

Young adults had the highest rate of mental woes (30 percent) while those aged 50 and older had the lowest rate (13.7 percent).

Overall, only 37.9 percent of adults with mental illness received mental health services.

While the use of mental health services was highest among those with serious mental illness (60.2 percent), 4.4 million adults with serious mental illness in the past year did not receive the services they needed.

"Too many Americans are not getting the help they need and opportunities to prevent and intervene early are being missed," SAMHSA Administrator Pamela S. Hyde said in an agency news release.

"The consequences for individuals, families and communities can be devastating. If left untreated mental illnesses can result in disability, substance abuse, suicides, lost productivity, and family discord. Through health care reform and the Mental Health Parity and Addiction Equity Act we can help far more people get needed treatment for behavioral health problems," she said.

Hyde was scheduled to present the survey findings at the World Conference on the Promotion of Mental Health and Prevention of Mental and Behavioral Disorders in Washington, D.C.

More information

The American Psychiatric Association has more about mental illness.