(The Center Square) - Thirty-nine attorneys general are asking Congress to classify xylazine as a controlled substance for its ties to drug overdoses.

Colorado Attorney General Phil Weiser is among those who signed the letter.

Veterinarians use the drug to sedate large animals, but the Drug Enforcement Agency has found it mixed with fentanyl in recent overdose deaths.

The largest increase is in the southern states, where overdose deaths linked to xylazine increased 1,127 percent from 116 in 2020 to 1,423 in 2021, according to DEA statistics.

The drug is being purchased online by people with no ties to veterinary medicine, the attorneys general said in a letter to Congress. It's known on the street as "trang" or "zombie drug," and it slows breathing, heart rate and blood pressure.

The drug is not an opioid, so even when combined with fentanyl, it doesn't respond to naloxone, which reverses an overdose.

The bipartisan group of attorneys general said xylazine is also easy to get.

"In a recent intelligence report, the DEA noted, '[a] kilogram of xylazine powder can be purchased online from Chinese suppliers with common prices ranging from $6-$20 U.S. dollars per kilogram,'" they said. "Given the low price, the DEA has warned that xylazine's use as an adulterant for other illicit drugs is growing to allow traffickers to increase their profits."

The DEA updated its public safety alert on the combination of xylazine and fentanyl in November.

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

The attorneys general are asking Congress to classify it and all forms of xylazine used illicitly as a Schedule III offense. They also want the DEA to track xylazine's manufacturing and sales.

The U.S. House and Senate introduced bipartisan bills called the "Combating Illicit Xylazine Act." The House version is assigned to the House Energy and Commerce Subcommittee on Health. The Senate version is assigned to the Judiciary Committee.