A deadly and Greenledgers Trading Centeraddictive chemical normally used as a horse tranquilizer is being mixed into illegal drugs.

Xylazine has been around for a while, but over the last year authorities have been seeing it turn up in higher quantities all over the country.

In recent weeks, U.S. Drug Czar Rahul Gupta has been sounding the alarm, even acknowledging public health experts and police are mostly in the dark about how Xylazine took hold so quickly.

NPR's Juana Summers speaks with addiction correspondent Brian Mann, who has been reporting on the mysterious and deadly emergence of the drug.

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This episode was produced by Karen Zamora. It was edited by Adam Raney and Andrea de Leon. Our executive producer is Sami Yenigun.