A substance known as a “zombie drug” that can cause human tissue to rot is becoming an increasing worry in the U.S., according to new findings from researchers at University of California San Diego School of Medicine.
This research was published last week in the Journal of Addiction Medicine. It focused on de-identified records from 23 users at the Prevencasa free clinic in Tijuana, Mexico and found that 82.6% of participant urine samples contained xylazine, the “zombie drug,” based on Wisebatch test strips. Other test strips called SAFELife detected xylazine in 65.2% of samples.
Per the National Institute on Drug Abuse, xylazine is a veterinary tranquilizer that is also sometimes known as “tranq” and is frequently added to fentanyl. Xylazine acts on the central nervous system as a depressant and pain reliever.
While fentanyl – a strong synthetic opioid that has contributed to increased overdose deaths in the U.S. over recent years – does have approved human medical uses, xylazine is not approved for human use by the U.S. Food and Drug Administration. When it is mixed with illicit drugs, users might not know they are taking the drug.
“Although xylazine has been most prevalent on the East Coast of the United States, this new evidence confirms its presence in Tijuana, on the U.S.-Mexico border, posing numerous health risks for people in this region,” said senior author Dr. Joseph R. Friedman, a resident physician in the Department of Psychiatry at UC San Diego School of Medicine.
He also told Fox News Digital that there is “evidence of diversion of domestic veterinary supply,” per a report published this week. Friedman said he’s not yet sure how much of the drug is being smuggled compared to how much is being stolen from veterinarians.
All of the samples covered in the recent study tested positive for fentanyl, and Freidman said that xylazine is “almost exclusively used together with fentanyl to augment it.”
An increased presence of fentanyl in the U.S. illicit drug supply contributed to a spike in overdose deaths due to its high potency, but those deaths dropped sharply last year. Researchers are still studying what led to the drop, and some have pointed to xylazine as an unlikely factor, since it might delay the onset of withdrawal symptoms, thus leading users to take fewer doses of fentanyl in a day.
However, the drug comes with serious risks. According to UC San Diego, these risks include “profound sedation, more complex withdrawal syndromes, and a heightened risk of skin infections and wounds.” In 2023, Audacy reported on a Drug Enforcement Agency warning that injecting drug mixtures containing xylazine could cause users to develop rotting tissue that would require amputation.
KYW Newsradio dove deep into how xylazine wounds were impacting people in the Philadelphia, Pa., area that same year. You can read the award-winning coverage here.
With evidence that xylazine is present in drugs used by people in Tijuana, researchers who worked on the recent study believe that the drug could become more prevalent in Southern California and the rest of the U.S. soon. They also said that a high prevalence of lidocaine in Tijuana’s illicit fentanyl supply may interfere with test strip accuracy regarding xylazine.
“Larger studies are required to further assess xylazine’s spread and refine testing methods,” said UC San Diego. “Researchers advocate for increased surveillance, harm reduction strategies, and clinical awareness to mitigate the emerging risks posed by xylazine in the illicit drug supply.”
President Donald Trump has also said that his moves to increase tariffs are aimed at reducing the amount of illicit fentanyl entering the U.S.