Mexican public health officials are sounding the alarm after a study found opioids containing the animal tranquilizer xylazine in a city in the country’s northwestern border with the United States.

Xylazine, known in English as “tranq dope” and “zombie drug,” is widely known as heroin and fentanyl and has fueled the opioid scourge in U.S. cities such as Philadelphia in recent years.

On April 8, the Mexican Ministry of Health and the Council on Mental Health and Addiction (CONASAMA) jointly issued an alert to health personnel and first responders in Mexican border cities about possible adulteration of heroin and fentanyl with xylazine.

Because xylazine is a sedative and not an opioid, it may make opioid overdose reversal treatments less effective and increase the risk of fatal drug poisoning, while also causing severe, life-threatening skin abscesses.

In Mexico, as in the United States, xylazine is only approved for use in animals, not humans.

The government alert noted that a study that tested 300 drug residue samples in the cities of Tijuana and Mexicali found xylazine, 35 heroin residues and 26 fentanyl residues mixed with fentanyl Adulterants in food.

This research, which is ongoing and not yet published, was funded by Mexico’s National Council of Science and Technology (CONACYT).
The study was designed to identify adulterants in the drug, rather than specifically looking for xylazine.

“We were surprised to find xylazine,” said Clara Fleiz, a researcher at Mexico’s National Institute of Psychiatry and the study’s lead author.

The alert comes amid signs that fentanyl consumption is spreading across Mexico. Fentanyl is a powerful synthetic opioid that causes tens of thousands of overdose deaths in the United States each year.