This study concluded that Massachusetts’ Medicaid managed care program substantially reduced the cost of substance abuse treatment over the first four years of implementation (1992 to 1996) by shifting 24-hour service out of hospital settings.  The authors note that Massachusetts increased access to treatment over the same period.   

Shepard, D. S., Daley, M., Ritter, G. A., Hodgkin, D., & Beinecke, R. H. (2001). Effects of a statewide carve out on spending and access to substance abuse treatment in Massachusetts, 1992 to 1996. Health Services Research, 36(6 Pt 2): 32-44.  http://www.ncbi.nlm.nih.gov/pubmed/16148959

Authors: Donald S. Shepard, Marilyn Daley, Grant A. Ritter, Dominic Hoddgkin, Richard H. Beinecke