I know for someone who is not used to fentanyl, a very very low dose can kill them, but again:

As harm reduction advocate Zoë Dodd noted, fentanyl is generally sold on the streets in 100-milligram increments.

“If you’re talking about Vancouver’s Downtown Eastside, fentanyl users are using a quarter gram [250 milligrams] or more a day,” according to Guy Felicella, a harm reduction and recovery advocate.

Unless I’m misunderstanding the article here, they’re talking about people who carry a SHITLOAD of fentanyl for personal use.