The term “zombie drug” describes Xylazine, a powerful non-opioid tranquilizer causing profound sedation and severe physical damage. Xylazine has rapidly infiltrated the illicit drug supply, particularly as an adulterant in fentanyl. Its increasing presence is escalating the dangers of the ongoing overdose crisis.
Xylazine: Identification and Intended Use
Xylazine is an alpha-2 adrenergic agonist, sharing properties with medications like clonidine. It was synthesized in 1962 as a potential antihypertensive agent for humans, but development was halted due to its tendency to cause severe hypotension and central nervous system depression. The U.S. Food and Drug Administration approved Xylazine for veterinary use in 1972. It functions primarily as a sedative, analgesic, and muscle relaxant for large animals like horses and cattle. It is sold legitimately as a liquid solution for injection.
This veterinary tranquilizer is now widely mixed into the illicit drug market, often referred to by street names like “tranq” or “tranq dope.” Illicit drug manufacturers use it as a cutting agent because it is low-cost and readily available. When combined with fentanyl, Xylazine extends the duration of the euphoric high, which is desirable for users who find fentanyl’s effects too brief. This addition effectively allows dealers to reduce the amount of fentanyl used while maintaining or enhancing the drug’s perceived effect, thereby increasing profit margins.
The Distinct Physical and Neurological Effects
Xylazine’s effects are profound and distinct from the opioids it is typically mixed with, causing severe central nervous system (CNS) depression. Neurologically, it induces deep sedation, drowsiness, and amnesia that can last for many hours, sometimes up to 72 hours, depending on the dose and combination with other substances. Users exhibit a stupor-like unresponsiveness, slow heart rate (bradycardia), and dangerously low blood pressure (hypotension).
The most physically distinctive effect—and the origin of the nickname—is the severe skin lesions associated with its use. Xylazine causes painful, slow-healing wounds, ulcers, and tissue necrosis that often appear at injection sites but can develop elsewhere. As an alpha-2 adrenergic agonist, the drug causes peripheral vasoconstriction, severely restricting blood flow to the skin and soft tissues. This lack of oxygen leads to tissue death, creating disfiguring ulcers highly vulnerable to secondary infections, often requiring aggressive medical treatment or limb amputation.
Complications in Overdose Treatment
The presence of Xylazine significantly complicates the standard emergency response to an overdose because it is a non-opioid. The overdose-reversal medication Naloxone (Narcan) does not counteract Xylazine’s sedative or respiratory-depressant effects. When an overdose involves Xylazine mixed with an opioid like fentanyl, Naloxone will only reverse the opioid component.
After Naloxone administration, the person may resume breathing, but they often remain deeply sedated, unresponsive, and at risk of airway compromise due to Xylazine’s lingering effects. This can create the misconception of a “Naloxone-resistant” overdose, potentially discouraging bystanders from administering the life-saving drug. In such cases, the medical response must be purely supportive, focusing on maintaining an open airway, providing rescue breathing, and managing the severe drops in heart rate and blood pressure. There is currently no FDA-approved human antidote or reversal agent for Xylazine intoxication, making supportive care the only available treatment option.
Public Health Context and Increasing Prevalence
Xylazine first gained traction in the illicit drug supply in Puerto Rico in the early 2000s, followed by its emergence in the Philadelphia drug market around 2006. Since then, its prevalence has rapidly increased, spreading across the United States. Data shows that between 2015 and 2020, Xylazine’s presence in overdose deaths increased nearly 20-fold across jurisdictions that conduct testing.
The substance has been detected in illicit drug samples in 48 out of 50 states, demonstrating a widespread geographic expansion. This rapid spread prompted the Biden-Harris Administration to designate the combination of fentanyl and Xylazine as an emerging threat to the nation in April 2023. Tracking the true scale of the crisis is difficult because many jurisdictions do not routinely test for Xylazine in toxicology screens, leading to an underestimation of its involvement in overdose fatalities.