Traces of a deadly new drug called “tranq” has been found in the bodies of overdose victims in San Francisco, authorities say.

Tranq, or xylazine, is an animal tranquilizer that authorities believe is added to illicit street opioids to heighten and prolong effects, particularly for fentanyl, which is known for short, but intense, highs.

The substance has been found in the drug supplies in eastern regions of the U.S. for years, but this is the first time it has been identified in overdose deaths in San Francisco, according to the San Francisco Department of Public Health.

Trace amounts of tranq were found in four out of 145 victims that were tested between Dec. 1, 2022, and Jan. 15 this year—and all involved fentanyl, according to the city’s public health department’s alert released Feb. 16.

The department said it is “working to understand” how prevalent tranq is on the streets and to “respond accordingly.”

The tranquilizer is known to cause severe skin lesions, leaving users open wounds that can lead to infections and even amputations.

“To date in San Francisco there have been no recent reports of increased severity of wounds or
syndromes consistent with xylazine intoxication or withdrawal,” the department stated.

Naloxone—a life-saving medication used to reverse the effects of opioids, more commonly known by the brand name Narcan—doesn’t work on tranq, because it’s not an opioid. However, the health department still recommends naloxone be administered in overdose cases because of the “high likelihood” that fentanyl is also involved.

While naloxone can restore breathing in an opioid overdose, the user “may still be somnolent or minimally responsive because of the ongoing effects of xylazine, which will gradually wear off,” according to the alert.

“People who are trained in naloxone should be reminded that the goal of an overdose reversal is to restore breathing, not to necessarily restore full consciousness,” the health department states.

Research shows deaths linked to tranq have spread westward across the country, especially in the northeastern states, according to the National Institute of Health. The institute states that from 2015 to 2020, the percentage of all drug overdose deaths involving xylazine jumped from 2 percent to 26 percent in Pennsylvania. Additionally, Xylazine was involved in 19 percent of all drug overdose deaths in Maryland in 2021 and 10 percent in Connecticut in 2020.