Federal authorities are warning Americans about an emerging public safety threat: fentanyl mixed with xylazine, a veterinary tranquilizer that's been linked to a growing number of overdose deaths across the country.

The U.S. Drug Enforcement Administration issued an alert Monday warning of a "sharp increase in the trafficking of fentanyl mixed with xylazine," which is also known as "tranq" or "tranq dope."

"Xylazine is making the deadliest drug threat our country has ever faced, fentanyl, even deadlier," said DEA Administrator Anne Milgram, adding that the DEA has seized xylazine and fentanyl mixtures in 48 out of 50 states.

The Centers for Disease Control and Prevention says 107,735 Americans died from drug poisonings between August 2021 and August 2022, and 66% of those deaths involved synthetic opioids like fentanyl.

Approximately 23% of fentanyl powder and 7% of fentanyl pills seized by the DEA in 2022 contained xylazine, according to Milgram.

The non-opioid tranquilizer is approved for animals but not for humans. The National Institutes of Health says studies show that people exposed to xylazine often used it in combination with other drugs — both unknowingly and intentionally, since some people report using fentanyl with xylazine "to lengthen its euphoric effects."

Repeated xylazine use is associated with skin ulcers and severe wounds — including necrosis, the rotting of human tissue — that could lead to amputation.

And mixing it with fentanyl places people at a higher risk of suffering a fatal poisoning, the DEA says.

Because the tranquilizer isn't an opioid, its effects can't be reversed by the opioid overdose antidote naloxone (aka Narcan). Public health officials worry that the spread of xylazine in the opioid supply could render naloxone less effective for some overdoses, the NIH says.

Experts still recommend administering Narcan if someone might be experiencing an overdose, especially since xylazine is so often combined with opioids. But people should know that it won't address the impact of xylazine on breathing, and call emergency medical services either way.

Xylazine is hitting the Northeast especially hard

Xylazine is a central nervous system depressant that can cause drowsiness and amnesia and slow a person's breathing, heart rate and blood pressure to dangerously low levels. People report injecting, snorting, swallowing and inhaling it.

Research suggests that tranq has been part of Puerto Rico's illegal opioid scene since the early 2000s and made its way to Philadelphia shortly after. It was first seen in toxicology reports there beginning in 2006, according to Substance Use Philly, a division of the city's health department.

Xylazine was found in over 90% of drug samples tested in Philadelphia in 2021, the program says. There are currently no validated drug-checking tests or tools for detecting xylazine; the health department got that data by testing drug samples with a forensic toxicology lab.

The problem has grown far beyond Philadelphia or even the entire state of Pennsylvania, which saw its percentage of overdose deaths involving xylazine jump from 2% to 26% between 2015 and 2020.

The NIH says overdose deaths linked to xylazine have spread westward across the U.S., including states like Texas and Ohio and hitting hardest in the Northeast.

It was involved in 10% of all drug overdoses in Connecticut in 2020, and 19% of all drug overdoses in Maryland in the following year.

There are efforts to address the growing problem

Federal agencies and lawmakers are taking steps to raise awareness and curb the spread of xylazine.

In November, the Food and Drug Administration distributed guidance to health care professionals warning of the risk of patients being exposed to xylazine in illicit drugs.

And it said in late February that it had taken action to restrict unlawful imports of the substance, making it subject to heightened FDA scrutiny and giving FDA staff the ability to detain any shipments that appear to be in violation of the law.

"We recognize the public health effects of xylazine tainting these illicit drugs and are continuing to ensure that legitimate product is restricted to veterinary use only," Tracey Forfa, the director of the FDA's Center for Veterinary Medicine, said at the time.

Dr. Rahul Gupta, the director of the Office of National Drug Control Policy, told CNN that the White House is looking into designating xylazine as a potential "emerging threat," which would trigger the development of a federal plan to address it.

Just this week, Senate Majority Leader Chuck Schumer held a press conference in Watertown, N.Y., to outline his plan to prevent xylazine-related overdoses, as North Country Public Radio reports.

The plan includes accelerating FDA efforts to track and eliminate illegal xylazine sources in the Northeast, increasing funding for a federal program that gives law enforcement agencies money to hire more officers and raising the budget for the Substance Abuse and Mental Health Services Administration.