This 2005 report evaluates Salt Lake County's adult felony drug court program. 

From the report:

The general effectiveness of drug courts on reducing recidivism has been consistently established (Belenko, 2001). The Government Accountability Office’s (GAO) review of adult drug court evaluations (2005) found that most studies have shown both during program and post-program (up to one year) reductions in recidivism. The evaluation of the Salt Lake County Drug Court is consistent with that overall finding.  In the 12 months following drug court exit, 19.7% of graduates had a new arrest, compared to 29.8% of the probationer comparison group and 46.5% of terminated client. The cost-benefit return for the drug court based on the Utah cost-benefit model (Fowles, et al., 2005) is approximately $4.29 return on every dollar invested in the program. This benefit takes into account both the explicit reduced costs to the taxpayer due to lowered recidivism and also the implicit reduced costs to potential victims due to lowered recidivism.

*Report no longer available.

Van Fleet, R. K., Hickert, A. O., and Becker, E. E. (2005). Evaluation of the Salt Lake County adult felony drug court program: final report. Criminal and Juvenile Justice Consortium, College of Social Work, University of Utah.