It would be easy to see that statistic as proof that fentanyl is “ultra-lethal.” But like any drug, fentanyl in the correct dose is not harmful at all. ( The problem arises when people who use heroin buy product that includes fentanyl in varying degrees. Thinking that they are using heroin, a less potent drug, they use a dose that is too large. That’s dangerous because a deadly dose of fentanyl is much smaller than a deadly dose of heroin. Before you take a doctor-ordered drug, you probably check to make sure that you are taking the right dose. People who use drugs bought in an illicit market don’t have that option — that’s the danger and that’s why fentanyl kills so many people. (This is why some people advocate for prescription heroin for people in addiction)