"Our best estimate is that on average, substance abuse treatment costs $1,583 and is associated with a societal benefit of $11,487, representing a 7:1 ratio of benefits to costs (9:1 when arrest data are “inflated” to proxy for actual crimes committed). This ratio is based on weighted average treatment costs, which reflect expected costs of treatment; 9-month follow-up of clients in all modalities with follow-up survey data, so that as many sources of benefit as possible could be included in the analysis; and benefit measures that demonstrate significant change, so that the estimates are robust to rare events. Sixty-five percent of the total benefit was attributable to reductions in crime costs, including incarceration. Twenty-nine percent was because of increased employment earnings, with the remaining 6 percent because of reduced medical and behavioral health care costs."

Source

Ettner, S. L., Huang, D., Evans, E., Ash, D. R., Hardy, M., Jourabchi, M., & Hser, Y. I. (2006). Benefit-cost in the California treatment outcome project: does substance abuse treatment "pay for itself"?. Health services research, 41(1), 192–213. doi.org/10.1111/j.1475-6773.2005.00466.x