Fentanyl is a man made copy cat drug. It copies heron and produces very very similar effects for example euphoria, sleeplessness, relaxation and the masking over of pain. It also causes constipation and confusion.
Authorities in the Uk have been discovering heroin mixed with Fentanyl and it is now cropping up in more areas.
Heroin is an all too powerful drug by itself. Drug dealers when dealing with new clients will usually sell pure and powerful heroin until they have a new client, a fully hooked addict.