Xylazine

Xylazine, known on the street as "tranq" or "tranq dope," is a sedative and muscle relaxant approved only for veterinary use (in animals such as horses and cattle) and never approved for humans — early human trials in the 1960s were abandoned because it caused dangerous drops in blood pressure and severe CNS depression. In recent years it has spread rapidly through the illicit drug supply as an adulterant, most often mixed into fentanyl. It is now one of the most common substances found cutting street fentanyl, which means many people are exposed to it without knowing. It matters here less as a drug people seek out than as a hidden contaminant of the opioid supply.

Xylazine is an alpha-2 adrenergic receptor agonist. By stimulating these receptors it reduces the release of certain neurotransmitters, producing sedation, muscle relaxation, and pain relief, along with slowed heart rate and lowered blood pressure. Crucially, it is not an opioid and does not act on opioid receptors — which is why the opioid-overdose antidote naloxone does not reverse xylazine's effects. When xylazine is mixed with fentanyl, naloxone can reverse the fentanyl but leaves the xylazine-driven sedation and breathing suppression untouched.

In people, xylazine produces heavy sedation, drowsiness, and a prolonged "blackout" state that can last for hours, along with slowed breathing, slowed heart rate, and low blood pressure. Because it is usually encountered mixed with fentanyl, its effects overlap with and prolong the opioid's sedation, which is part of why it has been adopted in the supply. People often have no idea they have taken it.

Xylazine adds two serious dangers on top of the opioids it is mixed with. First, because it is not an opioid, naloxone will not reverse its sedation or the breathing suppression it contributes — so an overdose involving xylazine may not fully respond to naloxone, though naloxone should still always be given for a suspected opioid overdose because fentanyl is usually present. Second, xylazine causes severe, distinctive skin wounds: open, necrotic ulcers that can appear anywhere on the body, not only at injection sites, are thought to result from the drug constricting blood vessels and starving tissue of blood, and in serious cases can become infected or lead to amputation. Repeated use also produces dependence and a difficult withdrawal. Xylazine test strips exist and can detect its presence in a drug sample. Because it is a hidden adulterant, the core risk is that people are exposed to all of this without knowing xylazine is there.

deepens sedation/respiratory depression when mixed with fentanyl; associated with severe skin wounds; NOT an opioid → naloxone does NOT reverse xylazine's effects)

FDA-authorized veterinary use only

emerging illicit adulterant; seized in xylazine-fentanyl mixtures in 48/50 states + DC

growing presence in illicit fentanyl supply