A veterinary tranquilizer that can cause serious wounds for regular users is spreading menace within the illicit drug supply. Xylazine, authorized only for animals, is one ingredient in an increasingly toxic brew of illicit drugs that killed a record of nearly 107,000 people in the U.S. in 2021. It is typically mixed with fentanyl, a synthetic opioid that itself has broadly infiltrated U.S. drug supply, including in supplies of cocaine and methamphetamine. Taken together, the volatile mixing means drug users often don’t know what’s in the substances they take.

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