The “zombie drug” is xylazine, a veterinary tranquilizer that has spread through the illegal drug supply in the United States over the past two decades. It earned the nickname because of the way it affects people: deep, prolonged sedation that leaves users slumped over in a trance-like state, often barely responsive for hours. It also causes severe skin wounds that can rot through tissue down to the bone, adding to the unsettling visual that gave the drug its name.
What Xylazine Actually Is
Xylazine is a sedative, pain reliever, and central nervous system depressant approved by the FDA exclusively for veterinary use. It was first synthesized in 1962, and early research explored whether it could work in humans. That research was abandoned after scientists discovered its tendency to cause severe tissue damage. For decades, it was used only in animal medicine, primarily to sedate horses, cattle, and other large animals.
It is not an opioid. This is a critical distinction, because xylazine almost always shows up mixed with fentanyl or other opioids in the illicit drug supply. Some people seek it out deliberately because it extends fentanyl’s euphoric effects, making a hit last longer. But many users report encountering it by accident, describing it as an unwanted additive they never asked for. Illicit xylazine first appeared in Puerto Rico in the early 2000s, where some users sought the intense sedation it produces. From there, it spread to the mainland U.S. and has been detected in drug supplies across the country.
Why It Causes Skin Wounds
The most alarming physical effect of xylazine is the development of necrotic skin ulcers, open wounds where tissue dies and decays. These wounds can appear at injection sites but also show up on parts of the body far from where the drug was injected, which has puzzled clinicians. Two mechanisms are likely responsible. First, xylazine appears to be directly toxic to tissue, creating a chemical burn effect. Second, it constricts blood vessels in the surrounding area, cutting off blood flow and oxygen. The combination of these two processes causes tissue to die, and with repeated injections, the wounds grow progressively worse.
These ulcers can become deep enough to expose bone and muscle. They resist healing as long as use continues, and they often become infected. The wounds are a major reason xylazine draws comparisons to krokodil, a homemade opioid that caused similar flesh-destroying injuries in Russia around 2012. Krokodil’s damage came from toxic byproducts in its crude manufacturing process, while xylazine’s wounds stem from the drug’s own pharmacological effects on blood vessels and tissue.
The “Zombie” Posture and Sedation
People under the influence of xylazine mixed with fentanyl often stand bent forward at the waist in what’s sometimes called the “tranq lean” or “tranq slouch,” nearly folded in half, sometimes with their hands almost touching the ground. They may remain in this position for extended periods, barely conscious. Researchers believe this posture may be related to a rigidity and stiffness of the back and torso caused by the drug combination. Fentanyl and similar synthetic opioids are known to cause “wooden chest syndrome,” a stiffening of the chest wall muscles that can make it difficult or impossible to breathe. This rigidity may make the bent-over position feel more tolerable than sitting or lying down.
Xylazine also slows breathing significantly. Because it depresses the central nervous system through a completely different pathway than opioids, its sedative effects layer on top of fentanyl’s respiratory depression, making overdoses more dangerous and harder to reverse.
Why Overdoses Are Harder to Treat
Naloxone (commonly known by the brand name Narcan) is the standard emergency treatment for opioid overdoses. It works by blocking opioid receptors in the brain. But xylazine is not an opioid, so naloxone does nothing to reverse its effects. When someone overdoses on a fentanyl-xylazine combination, naloxone may partially revive them by counteracting the fentanyl, but the xylazine-related sedation and breathing suppression will continue.
The CDC recommends that naloxone still be administered for any suspected overdose, because there’s no way to know in the moment whether opioids are also involved (and they almost always are). But additional steps are essential. Rescue breaths are especially important, since xylazine slows breathing to dangerous levels. First responders also recommend rolling the person onto their side into the recovery position and calling 911 immediately. More than one dose of naloxone may be needed to restore normal breathing, and professional medical treatment is necessary because field naloxone alone may not be enough.
How Common It Has Become
Xylazine’s presence in the drug supply has grown rapidly. Among 21 jurisdictions tracked by the CDC, the percentage of fentanyl-involved overdose deaths where xylazine was also detected rose 276% between January 2019 and June 2022, climbing from 2.9% to 10.9%. During that same broader period across 32 jurisdictions, xylazine was detected in nearly 4,900 fentanyl-involved deaths. Those numbers almost certainly undercount the true prevalence, because many toxicology screenings don’t routinely test for xylazine.
Withdrawal From Xylazine
Xylazine produces its own withdrawal syndrome, separate from opioid withdrawal. Symptoms typically begin 6 to 12 hours after the last use and include intense anxiety, irritability, restlessness, and a general sense of emotional distress. Within 8 to 24 hours, physical symptoms can escalate to rapid heart rate, high blood pressure, heavy sweating, and tremors. A hallmark of xylazine withdrawal is that taking more opioids does not relieve the symptoms, which distinguishes it from standard opioid withdrawal and can be confusing and frightening for people going through it.
Treatment typically involves a blood pressure medication that acts on the same type of receptor xylazine targets, helping to calm the nervous system. Clinicians also initiate standard opioid withdrawal treatment simultaneously, since most people using xylazine are physically dependent on fentanyl as well. Additional medications may be added for pain, agitation, or insomnia depending on symptom severity.
Legal Status
Despite its growing role in overdose deaths, xylazine is not a federally controlled substance in the United States. It is FDA-approved only for veterinary use, but possessing or distributing it doesn’t carry the same legal consequences as a scheduled drug like fentanyl or heroin. Federal legislation called the Combating Illicit Xylazine Act has been introduced to change this by placing xylazine under the Controlled Substances Act, but as of now it remains unscheduled at the federal level.
Several states have moved ahead on their own. Ohio classified xylazine as a Schedule III controlled substance in March 2023. Pennsylvania announced intent to temporarily schedule it the following month. West Virginia signed legislation classifying it as Schedule IV. Other state legislatures have introduced bills requiring xylazine testing in toxicology screenings, which would help track its spread more accurately.