Detection of Nitazenes (2-Benzylbenzimidazoles)-Novel Synthetic Opioids in Coronial Casework in Victoria, Australia

Background: The 2-benzylbenzimidazoles or nitazenes are an evolving class of highly potent mu-opioid receptor agonists. Nitazenes were originally developed in the late 1950s for pharmaceutical use as analgesics; however, due to their extreme potency and the risk of adverse health outcomes, pharmaceutical research was discontinued. Since 2019, nitazenes have emerged as illicit drugs of abuse, causing significant concern. From 2021, they have been detected in both coronial and clinical casework in Victoria, Australia. This study examined nitazene-related coronial casework in Victoria from 2021 to 2025 to explore the trends and characteristics of nitazene-related deaths. Methods: Relevant cases were identified from the Victorian Institute of Forensic Medicine's (VIFM's) case management system. Data were collated and analysed from all coronial cases where a nitazene was detected by a toxicological analysis between 1 January 2021 and 31 December 2025. Trend comparisons were made with nitazene detections reported in other countries. Results: Nitazenes were detected in 23 deaths from a total of approximately 33,108 coronial cases admitted to the VIFM for investigation over the time period. The age range was 17-45 years, with a median of 32 and with 87% of the deaths being male. The nitazenes detected were protonitazene (n = 14), metonitazene (n = 5), isotonitazene (n = 2), N-pyrrolidino etonitazene (n = 2), N-desethyl isotonitazene (n = 1), methylenedioxynitazene (n = 1) and etodesnitazene (n = 1). Two cases contained more than one nitazene; both involved protonitazene, one involved metonitazene, and the other involved N-desethyl isotonitazene and methylenedioxynitazene. The timeline of detection of these nitazenes displays similarities with emergence trends in other countries. The nitazene concentrations ranged from 0.1 to 33 ng/mL. Broad polydrug usage was evident in all cases, with other drugs co-detected in the blood including stimulants (particularly, methylamphetamine (48%) and cocaine (44%)) as well as pharmaceutical benzodiazepines (43%) and pharmaceutical opioids (22%), and 13% had 6-monoacetylmorphine detected in either blood or urine. Novel benzodiazepines (39%) were also common, including bromazolam, which was co-detected in 35% of cases. Nineteen deaths were attributed solely to nitazene-related mixed-drug toxicity, while the remaining four cases were attributed to cardiac- and pulmonary-related disease, with polydrug use deemed a contributing factor. Conclusions: This novel case series adds comprehensive toxicological information to the body of evidence reinforcing the high risk of harm associated with the use of nitazenes. It is imperative that toxicology services continue to monitor for nitazenes to promote community awareness against nitazene-related harm.