The emergence of the animal tranquilizer xylazine as a fentanyl adulterant, like the emergence of fentanyl as a heroin booster and substitute, has prompted law enforcement officials to agitate for new legal restrictions and criminal penalties. That response is fundamentally misguided, because the threat it aims to address is a familiar consequence of prohibition, which creates a black market in which drug composition is highly variable and unpredictable. Instead of recognizing their complicity in maintaining and magnifying that hazard, drug warriors always think the answer is more of the same.
Xylazine was first identified as a fentanyl adulterant in 2006, and today it is especially common in Puerto Rico, Philadelphia, Maryland, and Connecticut. In Philadelphia between 2010 and 2015, according to a 2021 BMJ article, xylazine was detected in less than 2 percent of drug-related deaths involving heroin and/or fentanyl. Its prevalence in such cases had risen to 31 percent by 2019. According to a 2022 Cureus report, “up to 78%” of illicit fentanyl sold in Puerto Rico and Philadelphia contains xylazine. In 2022, the Drug Enforcement Administration (DEA) reports, xylazine was detected in 23 percent of fentanyl powder and 7 percent of fentanyl pills analyzed by its laboratories.
Xylazine is a sedative, analgesic, and muscle relaxant that is not approved for use in humans but is commonly used by veterinarians. It is chemically similar to phenothiazines, tricyclic antidepressants, and clonidine. But like fentanyl and other opioids, xylazine depresses respiration, so combining it with narcotics can increase the risk of a fatal reaction. Unlike a fentanyl overdose, a xylazine overdose cannot be reversed by the opioid antagonist naloxone.
Xylazine also seems to increase the risk of potentially serious skin infections and ulcers that have always been a hazard of unsanitary injection practices. According to a 2022 article in Dermatology World Insights and Inquiries, “the presumed mechanism” is “the direct vasoconstricting effect on local blood vessels and resultant decreased skin perfusion,” which impairs healing.
Why is xylazine showing up in fentanyl? For the same reasons fentanyl started showing up in heroin. As a 2014 literature review in Forensic Science International notes, “illicit drugs, such as cocaine and heroin, are often adulterated with other agents to increase bulk and enhance or mimic the illicit drug’s effects.” Because xylazine and heroin have “some similar pharmacologic effects,” the authors say, “synergistic effects may occur in humans when xylazine is use as an adulterant of heroin.”