While you can often get the medical methadone/heroine programs they are not the norm in Europe. And they always come with the risk of a user falling back to the black market should the need arise. The availability and quantity of drugs is usually heavily restricted and don't allow for any lapses in daily routine or emotional affection. As a result methadone is readily available on the streets. I don't think such programs are a cure-all, merely a first step.
In Europe it does not only depend on the country but also on the city, which programs are available to addicts. The same goes for possession of minor quantities. Rules are highly confusing and it is usually safest to go by: "If you don't know the unspoken rules, try not to break the written ones."