"The percentage of recent drug users in State prison who reported participation in a variety of drug abuse programs rose from 34% in 1997 to 39% in 2004 (table 9). This increase was the result of the growing percentage of recent drug users who reported taking part in self-help groups, peer counseling and drug abuse education programs (up from 28% to 34%). Over the same period, the percentage of recent drug users taking part in drug treatment programs with a trained professional was almost unchanged (15% in 1997, 14% in 2004).
"Participation in drug abuse programs also increased among Federal inmates who had used drugs in the month before their offense, from 39% in 1997 to 45% in 2004. While there was no change in percentage of these inmates who had undergone drug treatment with a trained professional (15% in both years), the percentage taking part in other drug abuse programs rose from 32% in 1997 to 39% in 2004."
Mumola, Christopher J., and Karberg, Jennifer C., "Drug Use and Dependence, State and Federal Prisoners, 2004," (Washington, DC: Bureau of Justice Statistics, Dept. of Justice, Oct. 2006) NCJ-213530, p. 8.