A veterinary sedative used to knock out horses, dogs and wildlife is turning up in the US illicit drug supply, producing sedation so deep that patients describe feeling defenseless, and a withdrawal syndrome that standard opioid medications do not fully control.
That is the picture in a new report in Annals of Internal Medicine, based on interviews with 16 adults hospitalized with opioid use disorder and confirmed exposure to the drug, medetomidine.
Researchers from the University of Pittsburgh School of Medicine spoke with the patients between September and November 2025.
Interviewees reported extreme sedation that increased their vulnerability to harm, along with severe withdrawal that often required hospital care.
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The authors concluded that clinicians need greater awareness of medetomidine and treatment protocols tailored to it, since medications used for opioid withdrawal do not adequately relieve its symptoms.
What is medetomidine?
Medetomidine is a highly selective alpha-2 adrenergic agonist, meaning it acts on receptors in the nervous system that slow heart rate, blood pressure and breathing.
It is used in veterinary sedation and has no approved human medical use in the United States.
According to the Philadelphia CAMP drug-checking project, medetomidine is roughly 100 times more potent than xylazine, the previous animal sedative found in the illicit supply, and it was first noted to be clinically significant during a cluster of overdoses in Philadelphia in the spring of 2024.
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A CDC field report found the drug in 72% of illegal opioid samples tested in Philadelphia during the last four months of 2024, effectively displacing xylazine as the primary adulterant.
The overdose looks different
Because medetomidine is not an opioid, naloxone does not reverse its sedating effects.
First responders are still urged to give naloxone when someone is unresponsive, since fentanyl is typically present alongside the sedative, but the patient may remain heavily sedated even after opioid effects are blocked.
There is no FDA-approved reversal agent for medetomidine in humans.
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Rapid clinical tests for the drug are also not available, which means exposure is often confirmed only after treatment has begun.
Withdrawal that reads like a crisis
The withdrawal syndrome is what is catching emergency departments off guard.
In a CDC report from Pittsburgh covering October 2024 through March 2025, 10 patients with confirmed medetomidine exposure had a median peak heart rate of 165 beats per minute and a median peak systolic blood pressure of 200 mm Hg.
Nine of the 10 required intensive care, with a median hospital stay of about 93 hours.
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A separate CDC report from Philadelphia documented 165 patients across three health systems between September 2024 and January 2025.
Median heart rate reached 145 bpm and median systolic pressure 195 mm Hg.
Ninety-one percent needed ICU care and about one in four required a ventilator.
Dexmedetomidine, a related sedative given by infusion in the hospital, effectively controlled symptoms in 83% of the Philadelphia patients, and in nine of the 10 Pittsburgh cases.
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What clinicians and families should know
Standard buprenorphine and methadone regimens, the backbone of opioid withdrawal care, do not by themselves address the racing heart rate, spiking blood pressure and severe agitation seen with medetomidine withdrawal.
The Pittsburgh team is calling for stronger surveillance of the drug supply and treatment protocols built around this specific syndrome.
For family members and community responders, the practical message is that someone who has used street fentanyl and remains heavily sedated after naloxone may be under the influence of medetomidine as well, and anyone withdrawing from that same supply may need hospital-level care rather than home comfort measures.
A person with symptoms of severe withdrawal from illicit opioids should be evaluated in an emergency department.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.