I realize his isn't only in the US but the article focuses on US. I've seen warnings about this in Denmark. Especially about eto-nitazene:
Super-Potent Synthetic Opioids Spread Across US Amid Fentanyl Crackdown
Super-Potent Synthetic Opioids Spread Across US Amid Fentanyl Crackdown
40 times more potent than fentanyl and 500 times stronger than heroin.