Before revision: Gray death is a slang term which refers to the 2017 phenomena when potent mixtures of synthetic opioids, for example benzimidazole opioids or fentanyl analogues, often sold on the street misleadingly as "heroin".
After revision: Gray death is a slang term which refers to the phenomena that emerged in 2017, when potent mixtures of synthetic opioids, for example benzimidazole opioids or fentanyl analogues, often sold on the street misleadingly as "heroin".