SAN FRANCISCO (KRON) — A new illegal street drug known as “Tranq,” mixed together with fentanyl, caused the deaths of four San Francisco residents, public health officials confirmed on Thursday.

Xylazine, also known as “Tranq,” is a non-opioid tranquilizer that is not FDA-approved for human use. It was originally developed to be used for tranquilizing large livestock animals, such as cattle, according to the DEA.

“While xylazine has been circulating in the illicit drug supply on the East Coast of the United States for several years, SFDPH and OCME is seeing evidence of its presence in San Francisco for the first time,” the San Francisco Department of Public Health wrote Thursday. “Identifying xylazine in San Francisco is concerning.”

The four victims died between mid-December 2022 and mid-January 2023. Toxicology tests detected “Tranq” and fentanyl in their systems.

“Tranq” is commonly mixed with fentanyl, heroin, and other illicit street drugs, according to the DEA.

San Francisco public health officials were already struggling to stem the tide of a fentanyl overdose crisis when “Tranq” emerged this winter.

Fentanyl is a powerful and deadly opioid. In 2022, an average of 1-2 San Franciscans died every day from drug overdoses. Fentanyl, the primary driver of the overdose crisis in San Francisco, accounted for 72% of all overdose deaths last year, according to data from the city’s medical examiner.

Xylazine can cause excessive sleepiness and respiratory depression symptoms that appear similar to those associated with opioid use, making it difficult to distinguish opioid overdoses from xylazine exposure, public health officials said.

A lethal dose of fentanyl is shown in a DEA lab. (Image courtesy DEA)

Narcan, an opioid overdose reversal medication, has saved countless fentanyl users’ lives. But Narcan would not be able to save someone who overdosed with “Tranq” because it is not an opioid, experts say.

“With all the synthetic drugs out there, and the way they’re being mixed together, you never know what you’re actually buying,” warned DEA Intelligence Analyst Maura Gaffney.

Xylazine can be smoked, snorted or injected. It causes severe skin ulcerations that spread and worsen quickly. Repeated xylazine injection has also been associated with severe, necrotic skin lesions often requiring advanced wound care.

The Chief Medical Examiner’s Office wrote, “The OCME has not yet seen any … evidence that people in San Francisco are injecting xylazine. To date, SFDPH has not received any reports of skin wounds associated with xylazine, nor xylazine intoxication or withdrawal. These facts suggest that the drug may not yet be widespread, but SFDPH and its City and community partners are working to learn more, share information, and prepare street response teams to recognize the impacts of xylazine and respond appropriately. Coordination among City agencies is improving our surveillance of xylazine in the drug supply.”