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