Ethyleneoxynitazene (Tetrahydrofuranitazene) is a benzimidazole derivative which has been sold as a designer drug over the internet and presumably has opioid effects. It is an analogue of etonitazene where the 4-ethoxy group attached to the benzyl ring has been cyclised round to the 3-position to form a 2,3-dihydrobenzofuran ring system. It was first reported in Estonia in February 2023,[1] and subsequently in the UK in late 2023.[2]