Amid an ongoing opioid crisis fueled by fentanyl, researchers have discovered a new drug infiltrating the illicit market: the powerful veterinary sedative medetomidine. Used as an anesthetic for larger animals, medetomidine is 100 to 200 times more powerful than xylazine, the so-called “zombie drug.”
Withdrawal from medetomidine happens quickly and can cause tachycardia, extreme anxiety, nausea and vomiting, among other symptoms. To treat severe cases of withdrawal, patients need a medication called dexmedetomidine, an infused treatment that requires ICU stays because it can cause low heart rates and blood pressure.
Since treating these withdrawal symptoms is complex, an accurate idea of how many people are exposed to medetomidine and suffering from its withdrawal could help hospitals and their communities better allocate resources. A new analysis by researchers at the Perelman School of Medicine at the University of Pennsylvania found that patients suffering from medetomidine withdrawal has quadrupled in recent years.
In their study, published in JAMA Internal Medicine, researchers examined data from two Philadelphia hospitals dating from early 2020 through September 2025. Medetomidine’s emergence in fentanyl supplies has been traced anecdotally to the middle of 2024, so data was split to before and after that time to measure the drug’s ascent.
In the “pre-medetomidine period,” dexmedetomidine was administered to just shy of 6 percent of patients with opioid use disorder. But in the “post-medetomidine period,” roughly 20 percent of these patients required dexmedetomidine. In the last three months observed, that rate climbed to approximately 32 percent of those treated.
Patients suspected of medetomidine withdrawal were also significantly more likely to need other medications at higher doses. For example, 79 percent received methadone compared with 50 percent of patients with opioid use disorder who didn’t also require dexmedetomidine. Similarly, 36 percent of patients with medetomidine withdrawal received buprenorphine compared with 26 percent of non-medetomidine-related patients.
Additionally, patients who received dexmedetomidine logged more time in the ICU, on average, than other patients with opioid use disorder.
“Historically, heroin withdrawal without these adulterants could be managed in outpatient or minimally monitored inpatient settings,” said Ashish Thakrar, co-first author of the study and assistant professor of general internal medicine at Penn. “It was striking that, in the last quarter of our study, a third of patients required intensive care unit management for withdrawal from fentanyl mixed with medetomidine. Clinically, we recognize that we are in a new era of withdrawal management.”
Data from Penn Medicine