"Prior to the widespread availability of xylazine in the Philadelphia drug supply, it was often mentioned in passing by residents of the majority Puerto Rican neighborhood where our fieldwork was based as a powerfully psychoactive additive ‘“back on the Island”.’ Xylazine was occasionally detected in fatal overdoses in Philadelphia as early as 2006 (Wong et al., 2008), but it was not common knowledge among PWID. Significantly, however, many of our long-term informants recently immigrating/returning from Puerto Rico spoke with a mix of intrigue and apprehension about the psychoactive effects and health risks of 'anastesia de caballo [horse tranquilizer]'."
Friedman, J., Montero, F., Bourgois, P., Wahbi, R., Dye, D., Goodman-Meza, D., & Shover, C. (2022). Xylazine spreads across the US: A growing component of the increasingly synthetic and polysubstance overdose crisis. Drug and alcohol dependence, 233, 109380. doi.org/10.1016/j.drugalcdep.2022.109380.