This study suggests that behavioral health spending comprises 9.3 to 13 percent of Medicaid expenditures.  As a result of their literature review, the authors underscore the importance of monitoring future Medicaid behavioral health costs via the most accurate data available. 

Mark, T. L., Buck, J. A., Dilonardo, J. D., Coffey, R. M., & Chalk, M. (2003). Medicaid expenditures on behavioral health care. Psychiatric Services, 54(2): 188-94. 

Authors: Tami L. Mark, Jeffrey A. Buck, Joan D. Dilonardo, Rosanna M. Coffey, Mady Chalk

The full study is available from SAMHSA here: Medicaid Expenditures on Behavioral Health Care (PDF | 83.78 KB)