 Xylazine 101. Xylazine is a sedative drug that has been contaminating the US illicit opioid supply. It was discovered as an anti-hypertensive agent in 1962, but wasn't clinically used or FDA approved for human use due to hazardous side effects of sedation, hypotension, and bradycardia. Xylazine is currently only FDA approved for veterinary use as a procedural tranquilizer for large and small animals, where it is known as anisad, rompun, xylamed, sedazine, and chanazine. Xylazine is not an opioid but is a sedative with analgesic and muscle relaxant properties. When misused, it is often in conjunction with opioids, which was first documented in the early 2000s in Puerto Rico. Xylazine acts in the brain by inhibiting the release of dopamine and norepinephrine, causing central nervous system depression. While Xylazine has been noted as an adulterant primarily in fentanyl, it has been found contaminating other substances as well. Informally, Xylazine is referred to as Trank, Sleep Cut, or Anastasia de Caballo, otherwise known as horse tranquilizer. When mixed with other drugs, Xylazine can vary in color and texture, and similar to opioids, it can be swallowed, inhaled, smoked, snorted, or injected. Individuals with chronic exposure to Xylazine over time have experienced withdrawal symptoms, including anxiety, irritability, and restlessness. People exposed to substances containing Xylazine may experience symptoms similar to opioid intoxication, with some exceptions. Here are three considerations for harm reduction. First, Xylazine can make people very sleepy for many hours, putting them at risk of injury by lying on a limb in a position that could cut off circulation, or even being assaulted. It is important that people never use alone, and have a safe place to sit or lay down after using. Second, Xylazine may increase the risk of overdose. Because Xylazine is often mixed in the illicit opioid supply, naloxone should be administered as soon as possible in cases of overdose. As with all overdoses, call emergency services, administer naloxone, and make sure the individual is placed in the recovery position. Remember that naloxone only reverses the effects of opioids, so if Xylazine is present, it is common for people to continue to be sleepy after receiving naloxone. Third, individuals with chronic Xylazine exposure may develop skin wounds that take time to heal, regardless of how they used the drug. People who use drugs should be educated to watch for any atypical wounds on their skin, and seek medical attention for help treating wounds and monitoring for signs of infection. Based on limited national surveillance data, a rising prevalence of Xylazine in the illicit drug supply exists throughout the country. In places like Philadelphia, 91% of fentanyl and heroin samples tested contain Xylazine. Xylazine can be tested for in urine and blood at specialty laboratories, or detected in drug samples at local drug-checking labs. As the presence of Xylazine is increasing in the drug supply, it is critical to practice harm reduction and stay informed on the latest data and recommendations.