A Veterinary Tranquilizer Is Now in 1 in 4 New York Opioid Samples—and It Doesn't Respond to Narcan

A veterinary sedative used to tranquilize animals during medical procedures has quietly become one of the most common hidden ingredients in New York's illicit opioid supply, according to new peer-reviewed research from state and New York City health officials.

The drug, medetomidine, showed up in approximately one in every four opioid samples tested at community drug-checking sites across New York between May 2024 and December 2025. In May 2024 alone, detection peaked at over 44% of samples tested. The findings, published in NEJM Evidence, offer the clearest picture yet of how rapidly a new adulterant can take over a street drug market—and of the emerging human toll.

Preliminary death certificate data cited in the research identified 134 overdose deaths in New York City last year in which medetomidine was a contributing factor, up sharply from just 18 deaths the year before.

Medetomidine belongs to the same family of sedatives as xylazine, the animal tranquilizer better known as "tranq" that spread through the East Coast drug supply in recent years. Like xylazine, medetomidine is almost always found mixed with fentanyl, sometimes alongside its chemical cousin.

"It's one of the higher adulterants that you would see that's often associated with fentanyl," said Dr. David Holtgrave, an adviser to the state Department of Health commissioner and a co-author of the study. "Xylazine was an earlier one, also a veterinary tranquilizer, and this one has come close to that."

The emergence of medetomidine creates significant challenges for overdose response. Because the sedative does not act on opioid receptors, it does not respond to naloxone, the standard opioid-overdose reversal medication. Health officials emphasize that bystanders should still administer naloxone because fentanyl is usually present in these mixtures, but they must also stay with the person, protect their airway, and call 911.

Hospitals across New York have been seeing patients arrive in deep sedation, often with very low blood pressure and shaking, followed by severe withdrawal marked by racing heart rates, heavy sweating, and uncontrollable vomiting.

State and city officials first detected medetomidine in an upstate sample in May 2024 that had been sold as heroin but produced unexpected sedation. Within months, routine testing picked it up in more than 20% of opioid samples, and levels have remained around 30% in recent months.

In response, the state Department of Health began distributing 15,000 medetomidine test strips to partner organizations in January and has issued public alerts to drug users, harm reduction groups, and clinicians. The state's public drug-checking dashboard now tracks a growing list of adulterants, with officials planning to add new substances as tips come in from users.

The death toll figures remain preliminary. The study notes that cause and manner of death for 2024 and 2025 cases are still being investigated, and additional medetomidine-linked deaths could be identified. Researchers acknowledge that part of the documented rise may reflect expanded testing rather than a pure increase in prevalence, though the persistence of the drug in recent months suggests a real market shift rather than a testing artifact.

For Dr. Holtgrave, the deeper question is whether New York can catch the next unknown substance earlier than it caught this one. "We may not always know exactly the cause, why it has increased so much, but the first thing that we need to be able to do is to identify these trends," he said.

The research underscores the increasingly complex nature of the illicit drug supply, where new adulterants can emerge and spread rapidly, complicating both overdose prevention and clinical response. For New Yorkers who use opioids or know someone who does, the message from health officials is clear: carry naloxone, never use alone, and be aware that the drug supply now contains substances that standard overdose reversal medications cannot counteract.