Researchers at the University of California San Diego School of Medicine, in collaboration with the Prevencasa free clinic in Tijuana, Mexico, have solidified concerns surrounding xylazine, a powerful veterinary anesthetic increasingly mixed with illicit drugs. The alarming results of their study indicate the presence of xylazine in the drug supply at the U.S.-Mexico border, raising critical public health apprehensions. Published on March 20, 2025, in the Journal of Addiction Medicine, the study signals the urgent need for intervention in the region.
“Xylazine is a veterinary anesthetic that is not approved for human use and is increasingly detected alongside illicit fentanyl in parts of the United States and Canada,” said Dr. Joseph R. Friedman, senior author of the study and a resident physician in the Department of Psychiatry at UC San Diego School of Medicine. He noted that while xylazine has mainly been found on the East Coast, this latest evidence confirms its emergence in Tijuana, borderlining the U.S. and potentially endangering health in Southern California.
The study involved the analysis of de-identified records from 23 users at the Prevencasa clinic, where urine and drug paraphernalia samples were collected and tested for xylazine among other substances. The findings are stark: xylazine was identified in 82.6% of participant urine samples using Wisebatch test strips and in 65.2% with SAFElife test strips. Additionally, paraphernalia testing confirmed the presence of xylazine in 52.2% of samples through mass spectrometry. Alarmingly, 100% of participants’ urine tested positive for fentanyl.
Xylazine consumption is linked to severe health risks, including profound sedation, complex withdrawal syndromes, and a heightened risk of skin infections that may result in necrosis, particularly in those who inject the drug. The Centers for Disease Control and Prevention classify xylazine as presenting serious threats to users. Given Tijuana’s strategic position as a major conduit for drugs entering the U.S. market, researchers are urgently warning that xylazine could soon proliferate throughout Southern California.
“This study underscores the importance of expanding drug-checking efforts in border regions,” added Friedman. With incidents of xylazine rising, he emphasized the necessity for accessible testing tools, including xylazine test strips for both users and healthcare providers, to combat emerging risks associated with this substance.
The significance of the findings is compounded by a noted prevalence of lidocaine in Tijuana’s illicit fentanyl market, which researchers caution may affect the accuracy of xylazine test strips. More comprehensive studies are needed to standardize xylazine testing while understanding the rationale behind the introduction of lidocaine into drug mixtures.
The escalating xylazine trend aligns with broader patterns observed in the U.S., where illegal drug markets are facing increased adulteration. Philadelphia's epidemic illustrates this well; in 2022, approximately 34% of the city’s 1,413 overdose deaths involved xylazine, typically in combination with fentanyl. Reports from the Drug Enforcement Administration indicated that xylazine identifications spiked by 61% and 193% across eastern and southern states between 2020 and 2021, respectively.
Dr. Kimberly Sue, an opioids researcher at Yale University, commented on the broader implications of xylazine in drug adulteration. “If xylazine is becoming as common in certain parts of North America as this paper has found, we urgently need harm reduction treatments for exposure to xylazine.”
Friedman explained that drug cartels exploit xylazine's cheapness to stretch fentanyl supplies, hoping to retain or increase their profits while appealing to a customer base that is inclined towards longer-lasting highs associated with xylazine's effects. However, it brings forth serious complications for emergency care providers.
“It's been associated with some really gnarly wounds, soft tissue infection and destruction,” Friedman stated. “Users will get these terrible wounds on their legs.” The complications of overdose cases become more profound when xylazine is involved, as individuals may remain unconscious despite receiving naloxone, complicating rescue efforts significantly.
The study promotes the case for integrating educational campaigns targeting the public and healthcare professionals, focusing on xylazine's dangers. As the prevalence of this veterinary anesthetic grows within drug supplies, specialists recommend multidisciplinary approaches for treatment and harm reduction.
These findings present pressing challenges for public health in addressing the spread of xylazine along the U.S.-Mexico border, calling for timely responses and informed practices that can adapt to the ever-evolving landscape of illicit drug use.
