The drug xylazine, which has been linked to an increase in overdoses, has now been seized in 48 of 50 states, the Drug Enforcement Administration announced Monday in an alert.

Xylazine, also known as tranq, is often cut with fentanyl. Xylazine is legal as a horse tranquilizer, but it’s not approved for human use.

“Xylazine is making the deadliest drug threat our country has ever faced, fentanyl, even deadlier,” DEA boss Anne Milgram said in the alert. “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.”

Fentanyl is cut with xylazine to extend the high that users feel. The average fentanyl high is relatively short, but the sedative effects of xylazine can make it last longer.

However, xylazine itself is not an opioid, meaning that overdose-reversal drug naloxone, better known by the brand name Narcan, does not work on it.

Because xylazine is often found in opioids, medical experts still recommend administering Narcan and calling 911 when around someone suffering an overdose.

More than 107,000 people died from overdoses between August 2021 and August 2022, according to the Centers for Disease Control and Prevention. Two-thirds of those overdoses involved fentanyl, but the feds did not know how many also involved xylazine because medical examiners do not always test for it, and it doesn’t show up on basic toxicology screenings. Earlier this month, several people died of xylazine overdoses in Syracuse, New York, within a week.

The drug was detected in large quantities in Philadelphia before spreading across the country.