The Drug in ‘Tranq Dope’ Is Great for Horses but Horrific for Humans

Penny, a 3-year-old sorrel mare with a white blaze, had been slobbering her feed and fighting her bit, signs of a likely toothache. An exam confirmed that she needed two wolf teeth extracted and the sharp edges of some molars ground down, procedures that required propping her jaws open with a speculum.

To protect Penny from pain, and protect himself from the kick of a horse who outweighed him tenfold, Boyd Spratling, Penny’s veterinarian, gave her a shot of xylazine, a common animal tranquilizer. Within moments, her long neck drooped and her eyelids fluttered at half-mast. Forty-five minutes later, dental surgery done, Penny sauntered out of the clinic in rural Nevada and into her trailer.

To Dr. Spratling, xylazine is a vital analgesic and sedative, which he also occasionally uses in cattle, for procedures like C-sections in cows and penile injury repairs in bulls. It’s a staple for zoo veterinarians, too.

But in the last few years, the drug has also turned into something else: a cheap, addictive adulterant to illicit fentanyl that is contributing to the rise in overdose deaths around the country. The xylazine-fentanyl combo, known in the drug trade as “tranq dope,” is a life-threatening mix that depresses breathing, heart rate and blood pressure, and can cause blackened, chemical burn-like flesh wounds that can lead to amputation.

In a xylazine alert in March, the Drug Enforcement Administration said that in 2022, it had detected the drug in nearly a quarter of the confiscated fentanyl samples in 48 states.

Last week, the White House’s Office of National Drug Control Policy designated the drug mix as an “emerging drug threat,” a classification that requires the office to devise a governmentwide intervention plan. But addressing the threat is proving to be a tricky balancing act involving stakeholders in areas as disparate as addiction medicine, commercial livestock and law enforcement. The challenge is to walk a careful line by managing a drug that is essential for veterinarians but is fueling a public health crisis.

Law enforcement agents are pressing for xylazine to be listed as a controlled substance, which would criminalize distribution for human use. Currently, the police can’t arrest a person for sales or distribution of xylazine. Their resources to track down its production are modest. A controlled-substance designation would make a crucial difference, law enforcement officials said.

But veterinarians fear that if that happened, their access to the medicine would be heavily regulated. They would have to maintain separate logbooks for federal inspection. More worrisome: Production of a classified drug would require additional quality control and security measures so costly that a manufacturer could raise the drug’s price or just stop making it altogether.

“When we first starting seeing on the news that xylazine was being mixed with fentanyl, we were horrified,” said Dr. Spratling, who keeps his xylazine in a double-locked container.

But, he added, “let’s not shoot from the hip because then the people who really pay the price, regulatory-wise, are the ones who have been using it in a responsible manner all along.”

Some addiction medicine specialists and harm reduction groups have different worries. They fear that new tough restrictions could set off a domino effect of the sort that contributed to the fentanyl crisis, including criminal charges against people with substance use disorders.

Authorizing a drug to be listed as a federal controlled substance can be done either by Congress or jointly by the Food and Drug Administration and the D.E.A.

A state can also list the drug. On Tuesday, Gov. Josh Shapiro of Pennsylvania, where the Philadelphia neighborhood of Kensington is ground zero for tranq dope, announced that his administration was doing so.

A spokesman for the governor, Manuel Bonder, said Mr. Shapiro had decided to move ahead with the designation “rather than wait for any future possibilities in D.C.”

Xylazine was approved by the F.D.A. for veterinary procedures in 1972. Since then, it has been used for procedures on sheep, deer, elk and even cats and dogs, as well as on horses and cattle. Earlier trials in humans had been shut down because the drug led to respiratory depression, so manufacturers never sought approval for human use. Until now, there has been insufficient incentive to research its impact on people. Its causal relationship to the flesh wounds that can result from its use is not understood. And unlike the protocols for opioids, those for reversing tranq dope withdrawal or managing rehabilitation have not been standardized.

Last month, a bipartisan bill introduced in both chambers of Congress by members from rural states — including Nevada, Iowa, New Hampshire, California, Florida, Texas and Colorado — offered a compromise. Rather than listing xylazine as a controlled substance, the bill proposes that a person who employs it for “illicit” purposes — sales or distribution for human use — would face the same penalties as if it were listed as a Schedule III drug, including fines up to $500,000 and a first-offense sentence of up to 10 years in prison.

Controlled substances are classified according to medical need and potential for abuse and addiction. Schedule III includes buprenorphine, the medication used to treat opioid use disorder. By comparison, Schedule I includes heroin and L.S.D. Schedule II includes oxycodone and fentanyl, which can be prescribed for pain.

Legislators said this path represented a hard-fought middle ground for bipartisan buy-in and, they hope, a fast track to passage.

“We need to make sure that we make it illegal for human use because of the devastating impact we see, but I also know, working with cattlemen and the ranchers in my state, that they need to be able to treat their horses and large animals with this drug,” said Sen. Catherine Cortez Masto, a Nevada Democrat, who introduced the bill with Sen. Chuck Grassley, an Iowa Republican, and Sen. Maggie Hassan, a New Hampshire Democrat.

Their bill has been endorsed by veterinary, rancher and police associations. If enacted, it would require manufacturers to enhance xylazine record-keeping and send tracking reports to a D.E.A. database. Law enforcement agents could pursue dealers.

But it exempts the legal use of xylazine for “administration to nonhuman species.” With that carve out, veterinarians would not face the restrictions of a controlled substance.

Typically, domestic, veterinary-grade xylazine comes as liquid in a vial while bulk xylazine shows up as a cheaper powder, possibly imported. The F.D.A. already announced it was ramping up surveillance of imported xylazine.

Beau Kilmer, the co-director of the RAND Drug Policy Research Center, said, “It’s important to know where xylazine is being mixed. The D.E.A. reports finding empty xylazine bottles at U.S. stash houses, so some mixing is happening here, but does mixing in the U.S. account for the majority or minority of cases?”

But at this stage, he said, it was unclear what impact scheduling would actually have on human consumption and health.

Many harm reduction groups and drug policy experts question the long-term efficacy of scheduling xylazine.

The recent history of efforts to tighten controls on prescription painkillers highlights some of their concerns. As federal and state agencies imposed strict controls on prescription opioids, drug dealers and people who use drugs shifted to using illegal opioids — heroin, counterfeit pills and illicit fentanyl. Many people arrested as sellers are themselves dependent on those drugs.

Maritza Perez Medina, the federal affairs director of the Drug Policy Alliance, a nonprofit harm reduction organization, said she worried that criminalizing xylazine would not substantially address its problems. “Simply put: Crackdowns put us in a game of whack-a-mole. When we try to eradicate one drug, a new one comes up.”

Xylazine began appearing sporadically as an addictive substitute for heroin in the 2000s: In 2011, a study observed that people in farming areas of Puerto Rico were injecting horse anesthesia and developing serious lesions.

Around 2006, the drug was found in Kensington, the Philadelphia neighborhood, which has a substantial Puerto Rican population. Its use there began escalating around 2018, after which it spread throughout the Northeast, following the path of fentanyl.

Addiction medicine experts said their chief concern was abating the health dangers created by xylazine. They urged that newly introduced xylazine test strips, which people can use to check the drugs they buy, be as widely distributed as fentanyl test strips.

But Dr. Joseph D’Orazio, the head of medical toxicology and addiction medicine at Temple University Hospital in Philadelphia, which has treated hundreds of patients for the effects of tranq dope, says that street drugs are mixed with so many different additives that even test strips fall short of what is needed to save lives.

He said the immediate focus should be on developing better treatments to manage acute withdrawal from xylazine. “So many patients avoid or abandon treatment because our current medications are not adequate to combat the dose of fentanyl and xylazine found on the street.”

For his part, Dr. Spratling remains aghast at the wildfire that xylazine has become. “I’ve been using xylazine for 45 years, and I’ve never seen the skin ulcerations and lesions on a horse that people are getting. It’s terrible. I’m dumbfounded,” he said.

Penny, the young mare, not only sprang back from her xylazine shot but also quickly recovered from her dental surgery. Her spirits and mouth healed, she performed well a few weeks ago at a local county stock horse competition.

But Dr. Spratling, who uses xylazine at least a half-dozen times a week for procedures, is uneasy. He said that if the government were to regulate the drug for him and his colleagues, many veterinarians would have a simple response. “They’ll just stop using it,” he said.