"The primary purpose of these [drug court] programs is to use a court's authority to reduce crime by changing defendants’ substance abuse behavior. In exchange for the possibility of dismissed charges or reduced sentences, eligible defendants who agree to participate are diverted to drug court programs in various ways and at various stages in the judicial process. These programs are typically offered to defendants as an alternative to probation or short-term incarceration."

Source

"Adult Drug Courts: Evidence Indicates Recidivism Reductions and Mixed Results for Other Outcomes," Government Accountability Office, GAO-05-219, Feb. 2005, p. 3.
http://www.gao.gov/new.items/…