Methadone has been very successful in helping clean people, lowering the crime rates and the NICE guidelines suggest that although clinical quality diamorphine (top whack heroin) has less long term co morbidity risk, it's ability to wean people off is negligible. Methadone requires lowering the strength to avoid cold turkey, not chronic use. Sadly, it is gaining street value of its own accord. I attended a controlled drugs intelligence meeting for a large city only last week, and the police reported over 50 gallons unaccounted for (nicked) in a recent audit of chemists.

Incidentally, heroin is far cheaper to manufacture, but Methadone is lower risk for overdose.

Presumably the anecdotal impression Akenaton has is because methadone loses its edge when subjected to the Glasgow tradition of battering and deep frying it.