Xylazine, a Drug Adulterant Whose Use Is Spreading in the Human Population from the U.S. to the U.K. and All Europe: An Updated Review

Xylazine, commonly called "tranq" or "sleep cut", is a strong alpha 2-adrenergic agonist used in veterinary practice as a sedative, analgesic, and muscle-relaxing agent. It has never been approved by the Food and Drug Administration for human use, but its use by people is on the rise. In the last decades, due to its low cost and ease of availability, it has often been illicitly used due to its abuse potential as a drug for attempted sexual assault and intended poisoning. In addition, xylazine's presence in the human body has also been related to domestic accidental events. Generally, it is combined with multiple other drugs, typically by intravenous injection, potentiating the doping effects. Xylazine's mechanism of action is different from that of other illicit opioids, such as heroin and fentanyl, and it has no known antidote approved for use in humans. The combination with fentanyl prolongs the euphoric sensation and may heighten the risk of fatal overdose. Furthermore, it may cause adverse effects, including central nervous system (CNS) and respiratory depression, bradycardia, hypotension, and even death. Recent reports of xylazine misuse have risen alarmingly and describe people who become "zombies" because of the drug's harmful effects on the human body, including serious wound formation that could even lead to limb amputation. This paper is an extensive review of the existing literature about xylazine and specifically deals with the chemistry, pharmacokinetics, pharmacodynamic, and toxicological aspects of this compound, highlighting the most recent studies.