A report funded by SAMHSA examines 1997 spending data for patients receiving treatment for co-occurring mental health and substance use disorders in Oklahoma, Delaware and Washington State.

From the report:

The study estimated expenditures on clients with co-occurring M/SU conditions and compared those with expenditures on clients with a single type of disorder—mental illness (MI only) and substance-use disorders only (SUD only). "Clients with co-occurring disorders" were defined in this study to include patients who were either receiving both MI and SUD services or had both types of diagnosis recorded by a mental health or substance abuse treatment program during 1997.

The numbers reported are estimates of expenditures made for three states with mental health and substance abuse (MH/SA) treatment services through three types of State programs—mental health (MH), substance abuse (SA), and Medicaid agencies. The expenditure estimates did not capture the spending on treatment of MI and/or SUD that may have occurred outside these programs in other State government departments (e.g., corrections, education, or child welfare) or other public or private systems or entities.

The authors highlight the following key findings regarding co-occurring conditions in this setting: substantial prevalence, higher total costs, spending greater than the sum of two treatments, use of most costly services, higher use of medications for severe mental illness (SMI), different client characteristics, primary responsibility with MH/SA agencies, highest level of spending on outpatient but not inpatient, comparable spending levels with clients with MI alone, and higher spending for youth versus adults. 

Full report:  Expenditures on Clients Receiving Treatment for Both Mental Illness and Substance-Use Disorders: Results from an Integrated Data Base of Mental Health from Three State Medicaid Agencies in 1997 (PDF | 738.21 KB)

U.S. Department of Health and Human Services, Substance Abuse and Mental Health Services Administration (SAMHSA). (2006). Expenditures on clients receiving treatment for both mental illness and substance-use disorders: results from an integrated data base of mental health, substance abuse and Medicaid agencies for three states in 1997. Coffey, R.M., Dilonardo, J.D., Vandivort-Warren, R., Graver, L.J., Schroeder, D., Miller, K., Adamson, D. and Forhan, C.