Doctors in New York City are scrambling to find answers as a a cheap, flesh-rotting horse tranquilizer floods the city’s illegal drug market.

Xylazine, called “tranq” on the street, is mass-manufactured in China and has recently proliferated on the streets New York as well as San Francisco and Philadelphia.

The “zombie drug” causes skin lesions that look like flesh is being eaten off, sometimes down to the bone, and can slow a person’s heart and breathing until they stop, leaving users catatonic or dead.