In scientific research, xylazine is a component of the most common anesthetic, ketamine-xylazine, which is used in rats, mice, hamster, and guinea pigs. The accounts of the actions and uses of xylazine in animals were reported as early as the late 1960s and early 1970s. Since the early 2000s, xylazine has become popular as a drug of abuse in the United States and Puerto Rico. Xylazine's street name in Puerto Rico is "Anestesia de Caballo", which roughly translates to “horse anesthetic." The reasons that may explain why this drug has become increasingly popular are still unknown. Further research is needed to gain more information on the distribution of xylazine in the body, physical symptoms, potential treatments, and predictive factors for chronic usage.