Medetomidine, a powerful animal sedative used by veterinarians, is fast becoming the adulterant of choice for drug cartels pushing fentanyl on U.S. streets.

​Also known as “rhino tranq,” medetomidine is showing up more frequently than its cousin xylazine, a pain reliever, in the illicit drug supply in places such as New York City, Philadelphia, and Chicago, according to public health alerts.