The U.S. Drug Enforcement Administration (DEA) this week issued a warning about the widespread threat of fentanyl mixed with the veterinary tranquilizer xylazine, CNN reports.

Xylazine, also known as “tranq,” is a powerful sedative approved by the Food and Drug Administration for veterinary use. It is not an opioid and does not respond to the opioid overdose antidote naloxone, according to the DEA.

“Xylazine is making the deadliest drug threat our country has ever faced, fentanyl, even deadlier,” DEA Administrator Anne Milgram said in the alert. “DEA has seized xylazine and fentanyl mixtures in 48 of 50 states. The DEA Laboratory System is reporting that in 2022 approximately 23% of fentanyl powder and 7% of fentanyl pills seized by the DEA contained xylazine.”

The agency warned that people who inject substance mixtures containing xylazine can develop severe wounds that may lead to amputation.