"It eats up your flesh, like a crocodile," said Martin, a drug user in New York City, in a recent interview with AFP about his experience with xylazine.

Xylazine, an animal sedative known by the street name 'tranq,' is adding a new and horrific twist to the opioid crisis that has swept the U.S. in recent years. The drug is increasingly being mixed with highly addictive fentanyl, often without users' knowledge, resulting in a gruesome side effect: rotting flesh and wounds that don't heal.

The synthetic opioid fentanyl, which is 50 times stronger than heroin, was linked to more than two-thirds of the estimated 109,680 overdose deaths that occurred last year, according to numbers posted Wednesday by the Centers for Disease Control and Prevention (CDC).

More than 90 percent of Philadelphia's lab-tested dope samples were positive for xylazine, according to the data provided by the Philadelphia Department of Public Health in 2021. 

Synthetic drug use is on the rise

Xylazine is commonly encountered in combination with fentanyl but has also been detected in mixtures containing cocaine, heroin, and a variety of other drugs, according to an intelligence report from the Drug Enforcement Administration(DEA).

In the mid-1990s, the misuse of prescription opioid painkillers emerged as a significant cause of fatalities, eventually leading to a gradual shift towards heroin. By the year 2015, the number of deaths caused by heroin surpassed those caused by prescription painkillers and other substances. A year later, the more lethal fentanyl and its closely related compounds became the biggest drug killer.

Overdose deaths are often attributed to more than one drug. According to CDC, some people take multiple drugs, adding that inexpensive fentanyl is increasingly cut into other drugs, often without the buyers' knowledge.

According to DEA, xylazine was detected in around 23% of fentanyl powder seized by U.S. authorities last year. 

"Xylazine is making the deadliest drug threat our country has ever faced, fentanyl, even deadlier," DEA Administrator Anne Milgram said in a statement in March.

'The government was woefully late': Experts

Xylazine was first approved for veterinary use in 1971 and is used to sedate cows, horses, sheep, and other animals. 

Still, xylazine was detected in about 800 drug deaths in the U.S. in 2020 and more than 3,000 in 2021, according to the Drug Enforcement Administration.

National Public Radio (NPR) in the U.S. contacted many of the top street drug experts in the country last week. They all agreed the government was woefully late grappling with the spread of fentanyl and is now playing catch-up on xylazine.

A handful of states, including Ohio, Delaware, West Virginia, and Pennsylvania, have moved to classify xylazine as a controlled substance in May. 

This spring, The U.S. Congress proposed several bills to regulate xylazine and to fund research on the drug. The TRANQ Research Act, which requires the National Institute of Standards and Technology (NIST) to support research and other activities related to identifying xylazine, just passed Senate on Thursday.