Heroin with a small amount of fentanyl gives an extra kick to the heroin. Heroin dealers who don't include fentanyl are regarded to have an inferior product.

Heroin with a small amount of fentanyl gives an extra kick to the heroin. Heroin dealers who don't include fentanyl are regarded to have an inferior product. If the heroin is cut with too much fentanyl, your customers die. As mentioned in other replies, the problem with doing fentanyl directly is that it only takes a minute amount to kill, amounts that are difficult to measure.