This feels like one of those things that gets spread around americentric forums but either don't actually exist or is being extremely misrepresented.
I had a hard time finding recent articles, but the articles I did find all agree Heroin Assisted Treatment, HAT, was good for the addict and the community. It was more effective and cheaper than the alternatives. That said, of the ones I found, they sampled only treatment resistant patients. Meaning conventional means such as rehab & therapy had already been attempted and they failed. So it's like a last-straw form of treatment.