Xylazine is a drug used for sedation, anesthesia, muscle relaxation, and analgesia in animals such as horses, cattle, and other non-human mammals. Veterinarians also use xylazine as an emetic, especially in cats. It is an analog of clonidine and an agonist at the α₂ class of adrenergic receptor.

In veterinary anesthesia, xylazine is often used in combination with ketamine. It is sold under many brand names worldwide, most notably the Bayer brand name Rompun. It is also marketed as Anased, Sedazine, and Chanazine. The drug interactions vary with different animals.

Xylazine has become a drug of abuse in the United States, where it is known by the street name "tranq", and particularly in Puerto Rico. The drug is being diverted from stocks used by equine veterinarians and used as a cutting agent for heroin and fentanyl, causing skin sores and infections at injection sites, as well as other health issues. Fentanyl mixed with xylazine is known by the street names "sleep-cut, zombie drug and tranq dope."