Xylazine is a medicine used in veterinary (animal) medicine. It is NOT an opioid. It is a tranquilizer, sedative and pain reliever that is FDA approved ONLY for use in animal medicine. It has no FDA-approved uses for humans. In veterinary medicine, it is used as a component of diagnostic and surgical procedures in animals ranging from cats and dogs to horses and cattle.

In recent years, xylazine has been found as an adulterant in drugs of abuse often sold on the streets, such as in heroin or fentanyl. Although many of its effects are similar to opioids, chemically it is not an opioid;  therefore, naloxone is not known to be effective in reversing the toxic effects of xylazine.

Xylazine is structurally similar to a class of drugs known as phenothiazines. Xylazine also has chemical properties similar to other drugs like clonidine, levamisole and tizanidine and may have similar clinical effects. Similar to clonidine, it acts as an agonist at central alpha-2-adrenergic receptors in the brain. This causes a rapid decrease in the release of the neurotransmitters norepinephrine and dopamine. It may have effects on other receptors, but more research is needed.