Over the course of a few weeks, the bruise she was used to getting from injecting Fentanyl began to turn into a blackened substance. There must have been something in the supply.

The dealers that were switched didn't help. People said that everyone's drug was being cut with something that was very painful.

She said she would wake up crying in the morning.

In her shattered Philadelphia neighborhood, and increasingly in drug hot zones around the country, an animal tranquilizer called xylazine is being used to bulk up illegal drugs.

Xylazine can cause wounds to erupt with a dead tissue called eschar and can lead to amputation. Users are vulnerable to rape and robbery due to the effect it has on the brain. The high from the Fentanyl fades and people immediately crave more. xylazine resists standard overdose reversal treatments because it is not an opiate.

The most recent data shows that more than 90 percent of Philadelphia's samples were positive for xylazine.

Shawn Westfahl, an outreach worker with Prevention Point Philadelphia, said that it was too late for Philadelphia. Philadelphia's supply is very low. We need to tell our story if other places choose not to.

xylazine was found in the drug supply in 36 states. 25 percent of drug samples in New York City have xylazine in them. The xylazine alert was issued by the FDA.

ImageOutreach workers lean over and assist a man slumped in a wheelchair on a city sidewalk underneath a bridge.
Shawn Westfahl, center left, attended to a man who Mr. Westfahl believed had just injected tranq dope, in the Kensington section of Philadelphia.Credit...Hilary Swift for The New York Times
Tracey McCann is in recovery from tranq dope at a treatment center near St. Louis. “I’d wake up in the morning crying because my arms were dying,” she said.Credit...Neeta Satam for The New York Times

Xylazine's true prevalence is not known. Hospitals don't check for it. State medical examiners don't do it often.

There is a drug in a gray zone. It was approved by the F.D.A. 50 years ago and is not subject to strict monitoring. It has not been on the radar of federal law enforcement.

Ms. McCann began her descent with prescription drugs. She was addicted to painkillers after a car crash. She was introduced to heroin by her boyfriend while she was in rehab. Fentanyl was cheaper and more powerful than heroin. Philadelphia was ravaged by the Covid-19 epidemic in 2020.

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Understand how the drug affects you. Fentanyl is a drug that is very addictive. It is easy to overdose on a small amount. There is only a short time to save a person's life during an overdose with Fentanyl.

Don't go to unlicensed pharmacy. Fentanyl is found in many prescription drugs sold online or by unlicensed dealers. Only pills that were prescribed by your doctor are allowed to be taken.

You should talk to your friends and family. Fentanyl use can be prevented by educating your loved ones about it. Fentanyl can be found in pills purchased online or from friends. The aim is to establish an ongoing dialogue in short spurts.

You can learn how to spot overdoses. When someone overdoses on Fentanyl, their skin becomes bluish. Call the emergency number if you think someone is abusing drugs. If you are concerned that a loved one could be exposed to Fentanyl, you may want to buy Narcan, a medicine that can reverse an overdose in a matter of minutes.

She was evicted from her room last year. She said that she was better than sleeping on the sidewalk. A person next to her has been shot. She fought off the man with a box cutter. She saw people with tranq wounds that were covered with fleas and flies.

She said she couldn't get away from the drug.

Ms. McCann shows a photo of herself last summer shortly before she fled Kensington, when she weighed only about 90 pounds.Credit...Neeta Satam for The New York Times

Hundreds of people filled the streets around Prevention Point to exchange used needles for sterile ones. Over the past three years, the center's wound care clinic has seen a 313 percent increase in visits due to tranq.

Brooke Peder rolled her wheelchair to the exchange check-in and handed over a container filled with needles. Three of her family members died of overdoses. Her right leg had to be removed because of a tranq wound that bore into the bone.

Ms. Peder, who has been using drugs in the area for 13 years, said she wanted to warn newcomers to the area about the reputation of a drug market. All over the country, they come from. She said that many people arrive with money and pay locals to get drugs.

She stretched the bandage across her body. The sheared flesh was hot and red. She said she injects tranq dope several times a day. She was afraid that injecting in a new site would cause a new wound.

At an office at Prevention Point, Ms. Peder changed the dressing on her arm.Credit...Hilary Swift for The New York Times

She said that the tranq drug eats its victims. Self-destruction is at its best.

The combination of xylazine, a sedative, and usually an opiate, is called tranq dope. There isn't much research on xylazine in humans. It has been found in fatal overdoses where the drugs were present.

Xylazine was developed as a tranquilizer for animals. The drug caused respiratory depression and low blood pressure, so trials were stopped. The use of anestesia de caballo, also known as horse anesthesia, began in Puerto Rico in the 2000s.

There is a large Puerto Rican population in the area. The use of tranq began to escalate there and throughout the Northeast about a year and a half ago. According to some epidemiologists, bottles of domestic xylazine, purchased online with a veterinary prescription or diverted from veterinary supply chains, became popular as a cheap, easy opiate.

The new mix of drugs had an advantage over the old one, with a bag of heroin selling for $10 and a tranq for $5.

An encampment in the Kensington neighborhood.Credit...Hilary Swift for The New York Times
Used needles, Narcan sprays and abandoned belongings on Kensington Avenue.Credit...Hilary Swift for The New York Times

Costs went up. Kim wondered why after shooting up, she was falling over and then woke up and felt like she needed to get another shot.

Dr. Joseph D'Orazio, an expert in toxicology and addiction medicine at Temple University Hospital in Philadelphia, said that most people wish they didn't have xylazine. What is put on the street is what people need.

It's difficult to resuscitate an overdose where xylazine was involved. A dose of the overdose-halting medicine, which blocks or reversesopioid's effect on brain receptors, will address the Fentanyl but won't rouse a victim with xylazine. Rescuers may try another dose. Too much of the drug can cause a person to go into withdrawal.

When responding to an overdose, responders are advised to check the person's breathing, protect the head and airway, and call for a backup.

The withdrawal from xylazine continues even after the withdrawal from opioids is stopped. People use tranq dope for fear of getting sick, which includes headaches, double vision, nausea, numbness in fingers and toes, sweats, and body-rattling anxiety. Anti-anxiety drugs are usually used to treat the patient's symptoms.

Kim Barauskas said that right after she accidentally injected tranq into an artery, she felt like her hands had been dipped in acid. Her fingertips may need to be amputated.Credit...Hilary Swift for The New York Times

Doctors are confused by how xylazine causes wounds that look like burns. They can be found on shins and forearms.

Ms. McCann's forearms were oozing with tranq-scorched blood. Her only source of clean water was the public restroom.

She learned how to change bandages at Prevention Point's wound care clinic. She carefully trimmed the eschar.

She was down to 90 pounds when she caught a glimpse of herself. She said that she had to either do a lethal shot of xylazine or leave the area.

The only person who would allow her to use a cellphone was a man who lost his arm and leg in a tranq accident. He was still using a needle.

She decided.

In her fifth month at an intensive outpatient program, Ms. McCann is at a healthy weight and stunned by her progress. Her scars are a road map of being lost and found. She said that people might think her arms look ugly, but they don't know about tranq wounds. My arms look great to me.

Ms. McCann is now in her fifth month of sobriety and back to a healthy weight.Credit...Neeta Satam for The New York Times

Mr. Westfahl, who coordinates Prevention Point's overdose prevention team, handed out Narcan, a drug used to reverse the effects of an overdose, on the street. Local residents and shop workers scurried by some of the people on the street as he and another outreach worker visited them. There were people slumped against parking meters and in doorways. Three people are burning a blanket for warmth.

The two men gave away a lot of Narcan. They put blue Opioid reversal kits on the street poles, filled with gloves, Narcan, and plastic mouth guards, for anyone to grab.

Public health officials and clinics are in the early stages of figuring out how to resist tranq. xylazine is a controlled substance in Florida. Monitoring of prescriptions and suppliers of the drug would be more strict if there was a federal schedule.

The Drug Enforcement Administration has been in touch with the F.D.A. and looks forward to the completion of its scientific and medical evaluation and scheduling recommendation, according to an official with the Drug Enforcement Administration.

Mr. Westfahl, right, and Carlos Del Valle walked around the Kensington neighborhood handing out Narcan and directing people to wound care and needle exchange clinics.Credit...Hilary Swift for The New York Times
Sara Wallace-Keeshen, right, and Kristi Petrillo-Straub, Prevention Point nurses, put together wound care kits for patients. They dress casually rather than in hospital scrubs, hoping to appear nonjudgmental and approachable.Credit...Hilary Swift for The New York Times

If more support programs are not forthcoming, the public health experts questioned whether scheduling xylazine would alleviate its attendant problems.

The goal is to educate those who could be exposed so that they don't use alone. Many leaders in the harm reduction movement want supervised injection sites where people can use in safer conditions and have their drugs tested. There are only two places in the US where people can learn if their drugs include xylazine in 10 minutes.

The Philadelphia health department has reached out to clinicians who work with tranq patients.

Shame is an impediment to progress. Drug users feel too embarrassed to go to the emergency room because of their wounds.

The shame can be perpetuated by health care workers. Sara Wallace-Keeshen, a Prevention Point nurse who wears casual clothes instead of medical scrubs, hopes to appear nonjudgmental and welcoming.

Narcan kits and missing person signs are common sights in Kensington.Credit...Hilary Swift for The New York Times

Mr. Westfahl went down the street. A crowd shouted "Get the Narcan!" at the intersection of the two streets.

There was a man on the sidewalk.

Mr. Westfahl asked people to not use Narcan. He opened the man's mouth to make sure he didn't have anything to eat or drink. Mr. Westfahl put his head back to make sure his airway was open. He rolled his knuckles quickly up and down the man's chest, making a loud noise that can wake someone up. The man came to a screeching halt.

Mr. Westfahl and some people lifted him. He lurched in the cold wind. Two women put their hands in his jacket.

They kept him warm by securing his zip up. The three went back down the street.

Hilary Swift is a reporter.