KNOX COUNTY, Tenn. (WZTV) — A newly identified synthetic opioid has been linked to at least 16 overdose deaths in East Tennessee, according to preliminary toxicology tests from the Knox County Regional Forensic Center.

Officials say the drug, N-propionitrile chlorphine, also known as cychlorphine, appeared in nine overdose deaths between late October and December. As of mid-January, the substance had been associated with seven additional deaths.

Authorities say the drug has been detected primarily in cases where other substances were present, including methamphetamine and fentanyl.

Chris Thomas, chief administrative officer and director of the Knox County Regional Forensic Center, said the drug has been appearing more frequently in toxicology reports, though officials are still working to understand how widely it has spread.

“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,” Thomas said.

Initial cases were identified in Knox County before spreading to several nearby counties, including Roane, McMinn, Campbell, Union, Anderson, Claiborne, and Sevier counties, according to forensic officials.

Dr. Darinka Mileusnic-Polchan, the center’s chief medical examiner, said cychlorphine is not approved for clinical use and has never been authorized for sale on the medical market.

“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 Dr. Darinka Mileusnic-Polchan, chief medical examiner at Knox County Regional Forensic Center. “We do know it’s more powerful than fentanyl and that naloxone, or Narcan, does not completely block the effects of the drug and multiple doses may be needed to prevent an overdose.”

She said early findings suggest the substance may be more potent than fentanyl. Mileusnic-Polchan also said naloxone, commonly known by the brand name Narcan, may require multiple doses to counteract overdoses involving the drug.

Researchers say cychlorphine is part of a group known as new synthetic opioids, or NSOs, laboratory-made opioids that differ structurally from fentanyl and its analogues.

According to the Center for Forensic Science Research and Education, the drug may have first appeared in China in 2024 before spreading to Europe, Canada, and the United States by mid-2025.

The Knox County Regional Forensic Center first identified the substance in Tennessee in late November 2025 after it appeared in an overdose death in Roane County. Investigators later determined an earlier case in Knox County dated back to October.

Officials say the findings remain preliminary as investigators continue to study the substance and its role in overdose deaths.