Nitazenes

Group: Depressants Opioids

Nicknames: zenes, zines

Last reviewed: October 2026

History

Nitazenes are a class of synthetic opioids containing a 2-benzylbenzimidazole core and were first synthesised in the late 1950s by CIBA Aktiengesellschaft in Switzerland as experimental analgesics and potential alternatives to morphine. They were considered chemically significant at the time as the class does not contain a phenanthrene scaffold found in morphine, codeine and heroin, or utilises the 4-anilidopiperidine scaffold of fentanyl, but rather activates opioid receptors by a structurally distinct benzimidazole-based opioid pharmacophore.

Despite their high analgesic potency, no nitazene was developed into an approved human or veterinary medicine; their extreme potency and associated safety and formulation challenges are likely to have limited their clinical usefulness.

After the initial research period, nitazenes largely remained obscure, although occasional identifications of etonitazene and related compounds were reported in forensic and toxicological investigations from the 1960s to the early 2000s. The modern re-emergence of the class appears to reflect, in part, the exploitation of historical medicinal-chemistry literature by clandestine manufacturers. These compounds have subsequently been detected in heroin and other illicit opioid products, as well as in counterfeit tablets sold as prescription medicines such as diazepam and oxycodone. They are also being found sold as powders and nasal sprays.

Isotonitazene was reported through the European early-warning system in 2019 and was subsequently identified with increasing frequency in European and international drug markets. Since then, a growing number of analogues, including metonitazene, protonitazene and etonitazepyne, have been reported. The class now represents an evolving threat to the UK illicit drug supply, particularly because people may be exposed without knowing that the product contains a potent synthetic opioid.