What is the skin-rotting 'zombie drug' that has hit many US cities?

Last year, viral footage showing people unable to stand and acting weird on the streets of the United States sparked a conspiracy theory that they were affected by some "zombie virus." It turned out to be drugs, as many had expected.

Xylazine, popularly known as "tranq," "tranq dope," and "zombie drug," is a new deadly substance in town. Sedative-like symptoms—extreme sleepiness and respiratory depression—characterize the drug's use, resulting in videos of people unable to stand. What is even more concerning is that the medicine has more "zombie-like" effects.

The drug can cause raw wounds on the user’s skin that can spread rapidly with repeated exposure. It starts with ulcers, hardens into dead skin called eschar, and if left untreated, can result in amputation.

The non-opioid drug was first used to cut heroin. Later, it spread to Fentanyl, a deadly drug that can kill in even small amounts.

The main problem with the "zombie drug" is that if you overdose, your chances of reviving are limited. Because people do not respond to naloxone, or Narcan, the most commonly used overdose reversal treatment, Xylazine is lethal.

Xylazine was initially discovered in Philadelphia and quickly spread to San Francisco and Los Angeles. Another big issue is the possibility of overdosing in circumstances where the zombie drug has found its way into other substances.

Consumers of illegal drugs are dissatisfied. Those who have used the "zombie drug" have said that it has taken away "any kind of joy" that comes with getting high, according to the New York Post.

"I’d wake up in the morning crying because my arms were dying," Tracey McCann, who developed wounds near her opioid injection sites, told the New York Times.

"Tranq is zombifying people’s bodies," another user told Sky News. "Until nine months ago, I never had wounds. Now, there are holes in my legs and feet."