"On the left is a lethal dose of heroin, equivalent to about 30 milligrams; on the right is a 3-milligram dose of fentanyl, enough to kill an average-sized adult male."
https://www.statnews.com/2016/09/29/fentanyl-heroin-photo-fatal-doses/
https://www.statnews.com/2016/09/29/fentanyl-heroin-photo-fatal-doses/