I know people that are actively addicted to heroin and some are on methadone clinics. They regularly fail their drug screens for heroin because they just get their methadone and still use without having to worry about dealing with withdrawals. For the last 8-10 months (for which they've been shooting up the whole time), they've been coming up positive for fentanyl only, meaning the bags they've been buying have zero heroin in them anymore, just fentanyl and cutting agent. Addicts are developing tolerances for fentanyl quicker than heroin and also feeling withdrawal symptoms in a much shorter window of time compared to how long it takes for a heroin addict to begin to feel dope sick normally. So, Fentanyl is: potentially fatal it's so potent, atleast 2-3x more physically addicting than heroin, about half as cheap as heroin which is cheaper than ever already. Also in the past year cocaine deaths have spiked due to fentanyl laced coke.