"In addition, and important to criminal justice stakeholders and participants, themselves, is what happens to a person’s criminal charges after s/he successfully graduates from drug court. Recognizing that some courts may have multiple tracks for drug court participants with perhaps varying kinds of criminal justice outcomes, we asked courts what happens to the criminal charges for the majority of their participants after graduation (see Table 2- 3.33). Charges are dismissed in 46.3 percent of courts, charges are reduced in 7.3 percent of courts, and charges and the conviction are expunged in 7.1 percent of courts. The charges and conviction stand, but with a reduced sentence in 22.5 percent of courts."

Source

Rossman, Shelli B., et al., "Final Report, Volume 2: The Multi-Site Adult Drug Court Evaluation: What's Happening with Drug Courts? A Portrait of Adult Drug Courts 2004" (Washington, DC: Urban Institute, June 2011), p. 66.
http://nij.gov/topics/courts/…
https://www.ncjrs.gov/pdffile…