Fentanyl is supposed to be 100X stronger than Morphine.
Why would dealers cut an opioid with another opioid? Why not use something like quinine? Unless the quality of the Heroin is so low it needs the Fentanyl for its kick which means the dealers are killing people and are not exactly pharmacists.
I’m not an expert, however, years ago heroin equaled near instant addiction. I doubt that has changed.
morphine = long-acting, the active molecule in opium
fentanyl = short-acting, more potent synthetic morphine
Heroin was the first opioid derivative. It is supposedly less addictive than morphine. It is faster-acting and more potent than morphine.
Why are they so addictive? In many/most people, they induce an intense euphoria.
Think how many times dealers can cut it to reduce it to street grade.