What Is Xylazine? The Animal Tranquilizer That Makes Fentanyl Even Deadlier

The White House on Wednesday designated fentanyl laced with an animal tranquilizer called xylazine as an “emerging threat,” a designation that requires the government to coordinate a national response within 90 days.

This is the first time the Biden administration has used the designation for a substance since Congress implemented it in 2018.

Xylazine, also called tranq, is a potent animal sedative that has been increasingly mixed into black-market fentanyl. No matter how it’s taken, xylazine can cause long-term bodily damage. It often leaves users with severe skin ulcers, soft-tissue wounds, and necrosis, or premature skin death.

Xylazine first appeared in the Northeast, namely in Philadelphia, in 2019. In recent months, the drug has been increasingly used across the country. Between 2020 and 2021, overdose deaths involving xylazine increased by 1,127% in the South, 750% in the West, more than 500% in the Midwest, and more than 100% in the Northeast.

A fentanyl overdose can be reversed with naloxone, which the FDA made available for over-the-counter sale in its nasal spray form earlier this month. But there is no known antidote to a xylazine overdose.

With the emerging threat designation, the Office of National Drug Control Policy (ONDCP) said it would bolster its efforts to improve testing, treatment, and care for xylazine. It will also support research into the drug and curb the illicit supply.  

“While national overdose death numbers have flattened or decreased for seven straight months, xylazine is complicating efforts to reverse opioid overdoses with Naloxone and threatens progress being made to save lives and address the opioid crisis.” The White House said in a press statement.

It’s too soon to see how the policy will impact efforts to curb xylazine use and overdose on the ground, said Kimberly Sue, MD, PhD, assistant professor of medicine in the Program in Addiction Medicine at Yale University School of Medicine.

“We’ve been dealing with this and sounding the alarm for a while now,” Sue told Verywell.

Drugs Contaminated With Fentanyl and Xylazine Are Especially Deadly

Xylazine is often cut with opioids. It can “add legs” to a fentanyl high because it can mimic the effect of the opioid and last longer in the body than the fentanyl, according to Alixe Dittmore, a training and content development coordinator at the National Harm Reduction Coalition.

Fentanyl suppresses the respiratory system, slowing breathing sometimes to the point of unconsciousness. Xylazine, meanwhile, mainly acts to slow the nervous system.  

“[Xylazine] makes it just a little bit harder or take a little bit longer to come out of an overdose as someone administers naloxone,” Dittmore told Verywell.

When responding to an overdose, administering naloxone and giving “rescue breaths” can reverse the effects of fentanyl in a person’s system. If xylazine is also involved, the naloxone may keep the person alive by resuming their breathing, but they may remain sedated and unconscious.

“That’s why you need naloxone to be oversaturated in communities because the reality is, our drug supply has become quite contaminated,” Dittmore said.

Emergency medical service providers can provide care to revive someone who has overdosed on xylazine.

Improving Treatment Starts with Testing

Improving testing and making it more accessible at the local level is the first step toward addressing the overdose crisis, Dittmore said.

“You can’t treat folks if you don’t know what’s going on in their body,” Dittmore said.

Before someone uses a drug, they can test for the presence of fentanyl with a test strip. In March, BTNX, the major manufacturer of fentanyl test strips, said they developed and shipped out a batch of new xylazine test strips. The test strips aren’t yet commercially available.

Fentanyl test strips are illegal in 42 states due to drug paraphernalia laws, even though the Centers for Disease Control and other top public health organizations endorse test strip distribution.

Polysubstances—the deliberate or unintentional use of two or more substances—have become rampant in the black market. For instance, a powder sold as ketamine could contain cocaine and methamphetamines. A 2022 review found that among the overdose deaths associated with xylazine, 98% also involved fentanyl, 45% involved cocaine, 28% involved benzodiazepines, and 23% involved heroin.

“It puts us in a really hard position because we don’t actually know what people are using. What people say they’re using is full of other things,” Sue said. “It’s a very complicated and scary time, and I think it’s only going to get worse.”

Most of the existing research on xylazine was conducted in animal studies as human trials were shut down. Researchers still have a lot to learn about xylazine, including its addictive properties and withdrawal effects, Sue said.

Xylazine currently isn’t listed as a controlled substance, meaning the Drug Enforcement Agency doesn’t have a clear way to regulate it. Members of Congress in both chambers have introduced legislation to classify xylazine as a Schedule III substance.

Sue said she hopes xylazine curbing efforts will make use of existing harm reduction organizations and syringe service programs, rather than trying to address xylazine or fentanyl in silos.

In addition to clean syringes, these programs often offer treatment medication, mental health services, hot meals, and more.

“They’re the bedrock of caring for people who use drugs,” Sue said. “They’re already caring for people who are using xylazine and fentanyl and they build trust and relationships that are truly magical.”