Nitazenes, a class of synthetic opioids more potent than fentanyl, have been increasingly detected in the global illicit drug market, particularly within counterfeit medicines, causing intoxication and death. They represent a significant public health concern due to their high toxicity and their invisibility to conventional toxicological screening methods.

Five counterfeit oxycodone tablets were collected in Paris by a drug-checking service between February and May 2025. Visual inspection indicated the tablets mimicked authentic oxycodone “M30” formulations. Two tablets were received intact and three in powder form (ground beforehand). Analytical testing was conducted using LC-DAD, GC-MS, LC-MS/MS, and LC-HRMS. Quantification was performed by LC-MS/MS for 340 substances, including 163 new psychoactive substances (NPS).

No oxycodone was detected in any of the samples; instead, all contained the synthetic opioids metonitazene and protonitazene. Quantification showed that tablets contained between 3.2% and 6.0% metonitazene, with protonitazene present in smaller amounts (less than 0.2%). The estimated metonitazene content in intact tablets (n=2) ranged from 3.7 to 4.0mg, approximately equivalent to 23mg of fentanyl, far exceeding lethal thresholds.

These findings confirm the circulation of synthetic opioids in counterfeit tablets sold as oxycodone in Paris and its suburbs. The presence of multiple nitazenes underscores the complexity and risk of the current illicit market. Drug-checking services and toxicological analyses are essential for early detection and public health response. Enhanced surveillance, harm reduction, and regulatory coordination are urgently required to mitigate the growing threat of nitazene-related poisonings worldwide.