States are increasingly looking to restrict access to an animal tranquilizer showing up in supplies of illicit drugs and contributing to a growing number of human overdose deaths.

Pennsylvania's governor said Tuesday that his administration will add xylazine (pronounced ZAI’-luh-zeen) to the state's list of controlled substances, tightening regulations on the drug and allowing authorities to charge people who violate those rules.

Listing xylazine as a "schedule III" drug under Pennsylvania’s controlled substance law was expected to effect this Saturday.

"By scheduling it, we are giving greater tools to law enforcement and others to properly regulate, control and contain these drugs, make arrests and hopefully prosecutions," Democratic Gov. Josh Shapiro said Tuesday at a news conference in Philadelphia.

Three weeks ago, Ohio Gov. Mike DeWine, a Republican, signed an executive order that directed the Ohio Board of Pharmacy to immediately classify xylazine as a schedule III controlled substance.

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A schedule III designation in Pennsylvania and Ohio allows veterinarians to continue using the drug to sedate animals, but it puts veterinarians under tighter regulations on how it must be handled, tracked and stored.

Xylazine is already a schedule I controlled substance in Florida, meaning it is a crime to possess it or sell it in the state. The state's attorney general has urged the U.S. Drug Enforcement Administration to immediately add xylazine to the controlled substances list.

Opioid Crisis Xylazine Pennsylvania

Pennsylvania Gov. Josh Shapiro speaks before President Joe Biden at the Finishing Trades Institute, March 9, 2023, in Philadelphia. Shapiro said on April 18, 2023, that he is classifying a veterinary tranquilizer, xylazine, as a controlled substance. (AP Photo/Matt Rourke, File)

Last week, the U.S. Office of National Drug Control Policy named xylazine as an "emerging threat" when it’s mixed with the powerful opioid fentanyl.

Xylazine, first approved for veterinary use in 1971, is used to sedate cows, horses, sheep and other animals. Sometimes called "tranq," it increasingly is being added to fentanyl and heroin, officials say.

Officials are trying to understand how much of it is diverted from veterinary uses and how much is manufactured illicitly. It is not comprehensively tracked nationally, researchers say.

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Still, xylazine was detected in about 800 drug deaths in the U.S. in 2020 and more than 3,000 in 2021, according to the Drug Enforcement Administration.

In Pennsylvania, xylazine contributed to 90 overdose deaths in 2017, and 575 overdose deaths in 2021 Shapiro’s office said.