my background is in harm reduction and as far as I know there is no credence to these tales. There are people in the U.S. overblowing the fentanyl situation either to stoke fear or sometimes it's just well-meaning undereducated folks

fentanyl has generally speaking only made it's way into the supply of non-opioids like cocaine as the result of contamination, not intentional adulteration. When we talk about fentanyl, in reality what's out there is perhaps some true fentanyl but a lot of fentanyl analogues that are much more potent (lethal dose in the mcg range). Often the people moving heroin are also moving cocaine and other drugs, and using shared surfaces to weigh and cut the product for street use. They aren't properly cleaning surfaces and instruments and thus fentanyl is ending up in all sorts of powdered drugs

fentanyl on weed has probably happened in some instances of intentional poisoning of an individual but I'd file this under similar in risk to your child being given an edible, or candy with a razor blade on halloween