What measures have been taken in the past to provide rehab to drug users through governmental funding?

One of my few issues with Barack Obama's platform is a fraction of his stance on HIV/AIDS prevention. I don't understand why he believes in funding a needle exchange for drug addicts instead of using the funding to establish rehab centers and treatment. To me, it seems like that plan of action is only encouraging drug use instead of trying to eliminate it. Have there been past governmental attempts or acts to do this prior to the "needle exchange" idea?

: http://alcoholdrugstreatment.info/what-measures-have-been-taken-in-the-past-to-provide-rehab-to-drug-users-through-governmental-funding