[3] Xylazine is a common veterinary drug used for sedation, anesthesia, muscle relaxation, and analgesia in animals such as horses, cattle, and other mammals.

[10][11][12] Fentanyl mixed with xylazine is known by the street names "sleep-cut", "zombie drug", "Iso" and "tranq dope".

[1] Results from early human clinical studies confirmed that xylazine has several central nervous system depressant effects.

Xylazine's muscle relaxant effect inhibits the transmission of neural impulses in the central nervous system.

[18] In January 2025 Xylazine was banned in the United Kingdom due to necrotic wounds, and fatalities linked to illicit drug use.

Xylazine can be inhaled or administered intravenously, intramuscularly, subcutaneously, or orally either by itself or in conjunction with other anesthetics, such as ketamine, barbiturates, chloral hydrate, and halothane in order to provide reliable anesthesia effects.

[3] Xylazine diffuses extensively and penetrates the blood–brain barrier, as might be expected due to the uncharged, lipophilic nature of the compound.

[3] Other factors can also significantly impact the pharmacokinetics of xylazine, such as sex, nutrition, environmental conditions, and prior diseases.

This low price makes it attractive for dealers looking for a cheap additive that is addictive and not treatable with opiate withdrawal medications.

[35][36][28] Xylazine's street name in Puerto Rico is anestesia de caballo, which translates to "horse anesthetic".

[3][37] From 2002 to 2008, its use was associated with a high number of inmate deaths at the Guerrero Correctional Institution in Aguadilla, Puerto Rico.

[40] From November 2021 until August 2022, 80% of drug paraphernalia which tested positive for fentanyl at needle exchange programs in Maryland also contained xylazine.

[41] As of 2022, xylazine was almost invariably combined with opioids when used recreationally, and the drug produced a characteristic withdrawal syndrome which complicates treatment of addicted users.

[42][43] In April 2023, the Biden administration declared xylazine-laced fentanyl an official emerging drug threat to the nation, the first time such a label has been given.

A 43-year-old male was found dead at home with postmortem toxicology detecting heroin, cocaine, fentanyl and xylazine.

According to Seattle police officials, their patrol officers are now on alert for people collapsing due to tranq consumption.

[32] Police departments in 45 US states are preparing for wound care, overdose response, and creating educational materials for communities.

[12] The most common side-effects in humans associated with xylazine administration include bradycardia, respiratory depression, hypotension, transient hypertension secondary to α1-adrenergic receptor stimulation, and other central and hemodynamic changes.

[16] Other possible side-effects are areflexia, asthenia, ataxia, blurred vision, disorientation, dizziness, drowsiness, dysarthria, dysmetria, fainting, hyporeflexia, slurred speech, somnolence, staggering, coma, apnea, shallow breathing, sleepiness, premature ventricular contraction, tachycardia, miosis and dry mouth.

However, experts still recommend administering naloxone during suspected xylazine overdose because the drug is very frequently mixed with opioids like fentanyl.

[8] Human tolerance to xylazine varies widely, with toxicity and fatality occurring between doses of 40–2,400 mg (0.62–37.04 gr).

[51] As of 1998, the α2-adrenergic receptor antagonist atipamezole was used to reverse the effects of xylazine or the related drug dexmedetomidine in veterinary medicine,[52] but this is not an approved medical treatment for humans, despite Phase I clinical trials in 2005.

[53] As of 2001, the effects of xylazine in animals were also reversed by the analeptics 4-aminopyridine, doxapram, and caffeine, which are physiological antagonists to central nervous system depressants.

[1] As of 2014, multiple drugs have been used for therapeutic intervention, including lidocaine, naloxone, thiamine, lorazepam, vecuronium, etomidate, propofol, tolazoline, yohimbine, atropine, orciprenaline, metoclopramide, ranitidine, metoprolol, enoxaparin, flucloxacillin, insulin, and irrigation of both eyes with saline.

[1] Severe cases may require tracheal intubation, mechanical ventilation, gastric lavage, activated charcoal, bladder catheterization, electrocardiographic (ECG) and hyperglycemia monitoring.

[3] Physicians typically recommend which detoxification treatment should be used to manage possible dysfunction involving highly perfused organs such as the liver and kidneys.