According to the Substance Abuse and Mental Health Services Administration's National Survey on Drug Use and Health, approximately 20 percent of Americans experienced mental illness in the last year. And about 5 percent of the U.S. adult population, or 11.4 million people, suffered from a serious mental illness, which is defined as a mental illness that resulted in serious impairment and severely limited at least one major life activity.
Among those suffering from serious mental illness, the rate of substance abuse or dependence was over 25 percent, compared with 6.1 percent of those who had not suffered from mental illness.
