The problem is that fentanyl is very strong, and drug traffickers have very poor quality controls. The LD50 is 0.03 mg/kg in monkeys, so if humans are like monkeys, a 70 kg human has a 50% chance of dying after ingesting 2 mg of fentanyl. A 1 mg pill of pure fentanyl would be very tiny.
So drug traffickers mix the fentanyl with baking soda, tramadol, starch, whatever cheap additive they can get their hands on. Each trafficker adds more, to make the product nonlethal, but mostly to increase bulk, and increase profit. Unfortunately, they use blenders, kitchen mixers, and their bare hands. They don’t invest in pharmaceutical grade equipment.
The mix is very uneven, so when an addict takes a hit, he or she may either get no buzz at all, get a nice high, or die of an overdose. Each hit is like Russian roulette.
If only drug traffickers had better equipment, and quality controls. The way things are today, when you buy illegal drugs you don’t know what the hell you’re getting.