Credit: CFSRE
A new synthetic opioid that is 10x stronger than fentanyl has been identified in the fatal overdoes of 25 people in just the last few months. The state of Tennessee, specifically East Tennessee, is being hit the hardest.
The novel synthetic opioid is called N-Propionitrile Chlorphine, also known as Cychlorphine. It belongs to an emergent subclass of novel synthetic opioids often referred to as “orphine analogues” and bears structural similarity to other benzimidazolones, according to the Center for Forensic Science and Research Education (CFSRE).
N-Propionitrile chlorphine was first detected at CFSRE in mid-2024, but samples containing the NPS have increased significantly—especially in fatal drug overdoses—since mid-2025.
For example, CFSRE has identified N-Propionitrile in 25 blood specimens from fatal overdoses recently—the vast majority submitted in late-2025 and early-2026. In addition, N-propionitrile chlorphine has been tentatively identified in more than 100 toxicology cases at NMS Labs. The toxicology specimens originated from nine states across the United States, as well as three provinces in Canada.
The largest number of overdose cases tied to N-Propionitrile come from Tennessee. The Knox County Regional Forensic Center says the drug is responsible for nine overdose deaths between October and December 2025. As of mid-January, the drug was also linked to seven more deaths, according to preliminary toxicology tests.
“It’s showing up at an exponential rate and at this point, we don’t know if it’s a single batch and done with or if it’s the new future,” said Chris Thomas, chief administrative officer and director of the Knox County Regional Forensic Center.
In the analyzed samples, CFSRE detected N-Propionitrile chlorphine as both the sole opioid as well as alongside other drugs and NPS. Co-detection with fentanyl and methamphetamine was the most common, followed by bromazolam and phenazolam.
As experts continue to learn more about N-Propionitrile chlorphine, it appears to have originated in China in 2024 before moving to Europe, Canada and the U.S. in mid-2025.
“This isn’t a drug that has been approved for clinical use, and it’s never been clinically approved to be sold on the market,” said Darinka Mileusnic-Polchan, chief medical examiner at Knox County Regional Forensic Center. “It’s more powerful than fentanyl and naloxone does not completely block the effects of the drug and multiple doses may be needed to prevent an overdose.”