An animal tranquilizer is showing up in the nation's illicit drug supply

More than 40% of street drug samples tested in Rhode Island contained the animal tranquilizer xylazine, according to a new analysis out of Brown University. It’s the latest sign that the drug, which causes sedation and can lead to skin infections and overdoses, is continuing to spread through the illicit drug supply in the United States.

"I think xylazine is probably hitting the kind of critical mass where it is probably going to get to a lot more places," said Chelsea Shover, an assistant professor at the University of California, Los Angeles, who studies substance use and addiction.

Xylazine, often referred to as "tranq," concerns public health experts because it causes such heavy sedation, which can leave people exposed and vulnerable for long stretches of time. It’s not an opioid, so Naloxone — which can help treat opioid overdoses — doesn’t work to reverse its effects. Xylazine has become increasingly involved in overdose deaths in the U.S.

The drug was common recreationally in Puerto Rico and then started showing up in Philadelphia in the early 2010s, Shover said. For the last decade, it’s been mostly confined to Philadelphia, she noted. Over the past few years, it started appearing in other places — like in Massachusetts and New York City.

In November, the Food and Drug Administration put out an alert to health care professionals about the drug, warning that it’s been found as a contaminant in other substances like fentanyl and heroin.

New data indicates it’s prevalent in Rhode Island as well. A program called testRI — Toxicological and Ethnographic Drug Surveillance Testing in Rhode Island — analyzed 90 samples from donated drug samples. Forty of those samples contained xylazine.

None of those 40 samples were sold as xylazine and it was most commonly found mixed with fentanyl. The drug might be mixed in with fentanyl and other opioids because it extends their effects, Shover said.

But people who use drugs may not know if the fentanyl they’re purchasing is contaminated with this other drug, said Alexandra Collins, an assistant professor in the department of epidemiology at Brown University and one of the lead researchers on the testRI study.

Many people who use drugs and community workers in Rhode Island don’t even know what xylazine is, Collins said. "It was quite jarring, in my opinion, just how much we’re seeing," she said.

Public health experts are still trying to understand the drug, which was developed for animals and has not been studied rigorously in humans. That includes figuring out the best way to respond to overdoses that also involve xylazine, said Rachel Wightman, a toxicologist and assistant professor of emergency medicine at Brown University and another lead researcher on the testRI study.

Someone treated with naloxone after an overdose with fentanyl mixed with xylazine might stay sedated, for example, Wightman said. Naloxone would reverse the effects of the fentanyl but not the xylazine.

“They might start breathing again but stay sedated,” Wightman said.

People can also become physically dependent on xylazine, which creates complications for people who want to start using a medication to treat opioid use disorder, like methadone. When someone stops using fentanyl as part of that process, they’d also be stopping xylazine use.

"There is the potential for them to be experiencing a withdrawal syndrome," Wightman said. "We’re still trying to figure out the best way to manage that."

Doctors are also seeing ulcers and other wounds on people who use drugs contaminated with xylazine, so part of harm reduction efforts might now need to include giving people who use drugs information on wound care, Shover said. "They take a long time to heal," she said.

The United States has seen new drugs spread through the supply before — most recently with fentanyl and synthetic opioids, which took off in the late 2010s and is now responsible for tens of thousands of deaths from overdose per year.

Shover said she doesn’t think xylazine will do the same level of harm, even if it becomes a fixture in the drug supply.

"It’s a very different drug," she said.

But experts are still watching its growth closely.

"We’ve seen it grow exponentially," Shover explained. "It’s definitely something I'm monitoring and I know that a lot of my colleagues in other places are trying to get a sense of when it’s arriving and how big it is."