A potent animal tranquilizer is likely behind an increase in drug overdoses in Chicago this month, health officials warned on Monday. 

The overdoses happened between May 11 and May 14, and drug samples from those cases tested positive for elevated levels of medetomidine. This powerful veterinary tranquilizer is not approved for human use. 

Chicago health officials said medetomidine has not previously been detected in Chicago.

Animal sedatives combined with other drugs

The drugs tested in Chicago also contained other opioid and non-opioid sedatives, including fentanyl, heroin, xylazine, alprazolam, and netizens, officials said.

Medetomidine can cause respiratory depression, which can worsen when taken with other sedatives. 

Because medetomidine is not an opioid, Naloxone will not reverse the effects. Health experts said naloxone should still be used because fentanyl usually combines with other substances.

The drug first appeared in the illegal  U.S. drug supply in Philadelphia in April and in Pittsburgh earlier this month, according to the Center for Forensic Science, Research & Education. The drug surfaced in Toronto in December 2023.

Symptoms of overdose

People who overdosed experienced symptoms such as low heart rate and low blood pressure, in addition to symptoms of opioid overdose like low breathing and small pupils,” the city said in a health bulletin posted on Monday.

In March 2023,  the U.S. Drug Enforcement Administration issued a warning nationwide for xylazine, another animal sedative found in the recent samples. Like medetomidine, xylazine is not approved for humans and has no known antidote. 

The CBS 2 Investigators learned it’s been showing up in autopsies in Cook County for years.

 CBS 2 reviewed Cook County Medical Examiner’s Office data that showed xylazine-related deaths rising. 

In 2022, the Cook County Medical Examiner’s Office recorded 158 opioid-related deaths, where xylazine was listed as the primary cause of death. That’s up from 110 cases in 2021 and 30 cases in 2020.

For users who survive, it can also cause human skin to rot.