You do know that xylazine is an adulterant? It is put in there because it is tough to get cheap heroin and fentanyl tends to kill their client base a lot faster than tranq.

Tranq is cheaper because it is available for animals, and not 'seizing and destroying something while putting the people who possess it in prison' is a great market force for lowering prices.

Ergo, don't criminalize heroin and tranq stops appearing in it.