The potent animal sedative that’s replacing tranq in street drugs — and making fentanyl even more deadly
The drug can cause life-threatening withdrawal symptoms that often require intensive care. Stephen Yang
A dangerous new substance is spreading through America’s illicit drug supply, and health officials say it poses an unprecedented overdose threat.
The drug, medetomidine, is a powerful animal tranquilizer that has begun appearing with increasing frequency in street drugs across major cities, including Chicago, Philadelphia, and New York. Public health experts warn that it can closely mimic the effects of opioids like fentanyl — but with one critical and deadly difference: overdoses often do not respond to standard reversal drugs.
Medetomidine is a veterinary sedative commonly used to relax muscles and relieve pain during animal surgeries. It works by suppressing adrenaline release in the brain and body, causing profound sedation and slowed heart rate. While it is chemically similar to xylazine — also known as “tranq,” a veterinary drug that has been mixed into street drugs since around 2020 — experts say medetomidine is far more dangerous.
In fact, medetomidine can be up to 20 times more potent than xylazine, meaning even tiny amounts can have extreme effects. It is also inexpensive and easily obtained online through suppliers of veterinary medicines and research chemicals, making it attractive to drug traffickers.
Federal officials say criminal networks are deliberately adding these substances to increase addiction and profits. Frank A. Tarentino III, special agent in charge of the Drug Enforcement Administration’s New York Division, previously warned that combining fentanyl with even stronger sedatives like medetomidine can result in catastrophic overdoses and poisonings.
The drug was first identified in the U.S. illicit drug supply in 2021. By July 2024, it had been detected in drug samples or biological specimens in at least 18 states and Washington, D.C. Experts believe its presence has expanded significantly since then, along with the number of deaths linked to it.
Medetomidine causes heavy sedation that can last for hours and may lead to coma. Users often experience dizziness, extreme fatigue, shortness of breath, nausea, blurred vision, and confusion. However, doctors say the most severe danger often emerges during withdrawal.
Withdrawal from medetomidine can be so intense that patients frequently require admission to intensive care units. Symptoms may include extreme spikes in heart rate and blood pressure — high enough to cause brain damage — along with uncontrollable vomiting, tremors, and profuse sweating.
“Our ICUs have been overwhelmed,” said Dr. Daniel del Portal, an emergency physician and hospital administrator at Temple Health in Philadelphia.
In Philadelphia, medetomidine is now appearing more often than xylazine in the local drug supply. Medical professionals and outreach workers have begun referring to the surge in cases as “the withdrawal crisis.”
City health records show that during the first nine months of 2025 alone, Philadelphia hospitals recorded 7,252 emergency department visits related to withdrawal — a sharp increase from 2,787 visits during all of 2023.
Overdose response presents another serious challenge. Unlike fentanyl overdoses, medetomidine overdoses frequently do not respond to naloxone, commonly known as Narcan.
When patients overdose on a combination of opioids and medetomidine, naloxone can restore breathing but does not counteract medetomidine’s powerful sedative effects. As a result, patients may remain unconscious even after breathing resumes.
Doctors caution against repeated naloxone dosing in these cases. “Once patients begin breathing normally, additional doses of naloxone do not appear to help and may trigger opioid withdrawal,” wrote Dr. Kory London of Thomas Jefferson University and Dr. Karen Alexander in The Conversation.
Health officials continue to recommend naloxone for suspected opioid overdoses. However, if a patient begins breathing but does not wake up, experts advise against further doses and instead recommend rescue breathing — mouth-to-mouth resuscitation — until emergency responders arrive.
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