Huge numbers.
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.
http://health.usnews.com/health-news/family-health/brain-and-behavior/articles/2010/11/18/mental-illness-hit-1-in-5--us-adults-in-past-year.html