ST. PAUL, Minn., March 20 (UPI) -- The presence of xylazine, a horse tranquilizer increasingly found mixed with fentanyl in supplies of illegal drugs, is spreading to the U.S.-Mexico border area, according to a study released Thursday.
Xylazine, also known as "tranq," is a powerful non-narcotic sedative that the Food and Drug Administration has approved for veterinary use, but not for humans. Fentanyl or heroin mixed with xylazine places users at a higher risk of suffering a fatal drug poisoning, officials say.
People who inject drug mixtures containing xylazine also can develop severe wounds, including necrosis -- the rotting of human tissue -- that may lead to amputation in some severe cases.
While the prevalence of xylazine is increasing across the country, it has so far mainly been seen in the eastern and southern United States, where identifications of tranq in illicit drug supplies jumped by 61% and 193%, respectively, between 2020 and 2021, according to the Drug Enforcement Administration.
Philadelphia has been considered the the epicenter of the xylazine phenomenon. In 2022, some 34% of the city's 1,413 unintentional overdose deaths involved xylazine, while virtually every death where xylazine was detected also involved fentanyl, city officials found. They have responded by distributing free xylazine test strips to individuals and community-based organizations.
Now, a new study conducted by researchers from the University of California-San Diego School of Medicine and published Thursday in the Journal of Addiction Medicine, has provided evidence that xylazine appears to be working its way into western U.S. drug markets, as well.
The study found an alarming number of positive hits for xylazine among users of illicit drugs at a free clinic in Tijuana, Mexico, signaling what the authors call an "urgent need for public health intervention" along the southern U.S. border.
By looking at the de-identified records of 23 drug users at the Prevencasa free clinic in Tijuana, researchers found xylazine in 82.6% of participant urine samples using simple xylazine test strips made by the U.S. medical technology firm Wisebatch and in 65.2% using test strips made by SAFElife.
That result is raising alarms that fentanyl laced with xylazine -- sometimes referred to as "tranq dope" by users -- may be quickly spreading into Southern California and beyond due to Tijuana's status as a trafficking hub for international drug cartels.
Researchers called for an urgent awareness campaign and widespread availability of xylazine test strips in response.
"Philadelphia still has the highest rates of xylazine, but since then, it's spread to almost the rest of the country, although at much, much lower rates," senior study author Dr. Joseph Friedman told UPI. "So, physicians and people in public health out here in California are not really used to dealing with this.
"In much of the country there is very little expertise in dealing with xylazine, and many times people don't even know they're treating patients who've been exposed to xylazine because it's not usually tested for," said Friedman, a resident physician in the Department of Psychiatry at UC San Diego School of Medicine.
Criminal drug gangs use inexpensive xylazine to cut fentanyl to increase their profits -- its psychoactive effect allows them to reduce the amount of fentanyl used in a mixture. It's also attracting customers looking for a longer high, since xylazine is described as having many of the same effects for users as opioids, but is longer lasting than fentanyl alone, experts say.
Two things about use of xylazine as an adulterant, however, are "really concerning," Friedman said.
"It's been associated with some really gnarly wounds, soft tissue infection and destruction," he said. "They're really damaging. Users will get these terrible wounds on their legs. The other thing is that xylazine complicates what an overdose on opioids looks like."
Users who overdose on opioids laced with xylazine can remain asleep due to its sedative effects, even after the overdose is reversed by using naloxone, thus greatly complicating efforts to save patients' life.
"Our team has had to develop and implement a set of protocols to handle xylazine-involved overdoses," Friedman said, adding that treating such patients takes significantly longer to accomplish than traditional overdose responses because life-saving measures need to be maintained while the victim remains asleep.
The findings support the need for expanded drug-checking efforts in border regions and show the importance of getting xylazine test strips into the hands of drug users and healthcare providers so they can reduce exposure risks, he added.
Xylazine's presence in illicit drug supplies raises the risk of "unpredictable health consequences" for users, such as low blood pressure, low heart rate and necrotic skin wounds, said opioids researcher Dr. Kimberly Sue, an assistant professor at Yale University School of Medicine and former medical director of the National Harm Reduction Coalition.
Sue, who was not involved with the UC San Diego study, echoed concerns that xylazine could be causing dependence or a new type of withdrawal syndrome, although that has yet to be confirmed.
"Research should be focused on understanding its prevalence in real-time, as this paper has shown, as well as the effects on individuals, why they use or avoid xylazine, and if there is such a thing as xylazine dependence or withdrawal symptoms from continuous use of xylazine," she told UPI.
"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 and multidisciplinary treatment approaches to xylazine wounds," Sue added.