Hospitals are struggling to care for growing numbers of behavioral health patients, and a new report explains why. In 2010, 20 percent of American adults aged 18 or older experienced mental illness (defined as having a diagnosable mental, behavioral or emotional disorder). The rate of mental illness was more than twice as high among those aged 18 to 25 (29.9 percent) than among those 50 and older (14.3 percent). Adult women also were more likely than men to have experienced mental illness (23.0 percent vs. 16.8 percent).

The report, from the Substance Abuse and Mental Health Services Administration's National Survey on Drug Use and Health, also shows that 5 percent of the population suffered from serious mental illness. SMI is defined as an illness that results in serious functional impairment that substantially interferes with or limits one or more major life activities.

About four in 10 people experiencing any mental illness in the past year received mental health services. Among those experiencing SMI, the rate of treatment was 60.8 percent.

The report also found that rates for substance dependence were far higher for those who had experienced mental illness in the past year. Adults experiencing any mental illness 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. Those who had experienced SMI in the past year had an even higher rate of substance dependence or abuse (25.2 percent).

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