Introduction: Nitazenes are potent synthetic opioids. Following reports questioning their post-mortem stability, nitazene-related deaths may have been underestimated in the United Kingdom. We investigated this using a rat model and regional coronial data, and also present national pharmacoepidemiologic trends in nitazene-related deaths.

Method: In vivo/ex vivo study: Anaesthetised Wistar rats (n = 12) received intravenous nitazene (metonitazene, N-desethyl isotonitazene, or N-pyrrolidino etonitazene). Rats were euthanised 15 min post-administration if cardiorespiratory arrest had not already occurred (n = 8). Blood and urine were collected, with repeat blood samples taken following cadaver refrigeration (4 °C) for one week. All samples were immediately frozen (−80 °C). Upon defrosting, half were analysed immediately by liquid chromatography tandem mass spectroscopy with half stored at 4 °C for 1 month before analysis.

Pharmacoepidemiology: Nitazene deaths were extracted from the National Programme on Substance Use Mortality in March 2025 along with all deaths from the Birmingham & Solihull coronial area (2019–2023). Descriptive analyses were conducted along with exponential smoothing models to compare observed and forecasted deaths in Birmingham & Solihull in 2023.

Results: In vivo/ex vivo study: A small fraction of the nitazene detected in the immediate post-mortem blood sample remained in the post-mortem day 7 blood sample that had been refrigerated for 1 month.