"Facilities were asked to estimate the proportion of clients in treatment with diagnosed co-occurring mental and substance abuse disorders.
"• On March 30, 2012, 46 percent of clients who were in treatment had a diagnosed co-occurring mental and substance abuse disorder.
"• The highest proportions of clients with co-occurring mental and substance abuse disorders were in federal government-operated facilities (61 percent) and in facilities with a primary focus of mental health services (74 percent)."

Source

Substance Abuse and Mental Health Services Administration, National Survey of Substance Abuse Treatment Services (N-SSATS): 2012. Data on Substance Abuse Treatment Facilities. BHSIS Series S-66, HHS Publication No. (SMA) 14-4809. Rockville, MD: Substance Abuse and Mental Health Services Administration, 2013, p. 34.
http://www.samhsa.gov/data/DA…