Nitazenes

2-benzylbenzimidazoles: a benzimidazole core with a benzyl group and a basic side chain, from an analgesic research programme that never produced a marketed medicine. They are full μ agonists, and potent — potent enough that the family sits in a different weight class from the material it is usually sold as. Names within it differ by one substituent (metonitazene, protonitazene, etonitazene, the N-desethyl and N-pyrrolidino variants) and those substituents change potency substantially, so a name is a poor guide to what a sample will do.

They are a separate family from the fentanyls because the scaffold is unrelated, and that has a practical consequence: fentanyl test strips are raised against the fentanyl structure and do not reliably detect nitazenes, so a negative strip says nothing about them. Respiratory depression comes on quickly, and reversal has repeatedly needed more naloxone than expected.