fentanyl and rc fentanyl derivitives in heroin is by no means a new thing, but carfentanil is the first veterinary used fentanyl derivative i have heard of. some seized heroin is mixed with it, some only contains no heroin only carfentanil! i know some people re going to seek it out just to check elephant tranquilizer off their list 
https://www.youtube.com/watch?v=yOGmb6zdPAM

https://www.youtube.com/watch?v=yOGmb6zdPAM
