This report analyzes the state of Washington's substance abuse and mental health problems and the potential impacts, including the economic benefits, of expanding M/SU treatment.  

From the report:

The Washington State Institute for Public Policy was directed by the 2005 Washington Legislature to estimate whether “evidence-based” treatment for people with alcohol, drug, and mental health disorders offers economic advantages. Do benefits outweigh costs? And, if so, what is the magnitude of the potential fiscal savings to government, as well as the total net benefits to all of Washington?

1. Evidence-based treatment works. We found that the average evidence-based treatment can achieve roughly a 15 to 22 percent reduction in the incidence or severity of these disorders—at least in the short term.
2. The economics look attractive. We found that evidenced-based treatment of these disorders can achieve about $3.77 in benefits per dollar of treatment cost. This is equivalent to a 56 percent rate of return on investment.  From a narrower taxpayer’s-only perspective, the ratio is roughly $2.05 in benefits per dollar of cost.
3. The potential is significant. We estimate that a reasonably aggressive implementation policy could generate $1.5 billion in net benefits for people in Washington ($416 million are net taxpayer benefits). The risk of losing money with an evidence-based treatment policy is small.

Full report: Evidence-Based Treatment of Alcohol, Drug and Mental Health Disorders (PDF | 386KB)

Washington State Institute for Public Policy (2006). Evidence-based treatment of alcohol, drug and mental health disorders: potential benefits, costs, and fiscal impacts for Washington State. Washington State Legislature Document No. 06-06-3901.