The Centers for Disease Control and Prevention on Thursday issued a health advisory warning of rising reports from U.S. jurisdictions detecting veterinary sedative medetomidine in the illegal drug supply.

The CDC and the White House Office of National Drug Control Policy warned public health professionals, clinicians, laboratorians and people at risk for overdose after medetomidine was detected in the fentanyl supply and linked to a severe withdrawal syndrome from exposure to it.

Medetomidine, which is also known as 'rhino tranq,' or 'dex', is not approved for human use but is approved for sedation and analgesia in dogs.

The agencies said it has increasingly been detected in law enforcement drug seizures, drug product and paraphernalia samples and wastewater samples, with the highest concentrations in the Northeast region.

The CDC said stopping medetomidine after regular use can trigger severe withdrawal, with symptoms including hypertension, anxiety, nausea, vomiting and fluctuating alertness, which may require emergency or intensive care. It can also cause profound sedation, slow heart rate and hypotension.

Because fentanyl is involved in most overdoses involving medetomidine, opioid overdose reversal medications like naloxone should be administered to restore normal breathing, the agencies said.

Medetomidine was first identified in the illegal drug supply in 2021 and began appearing sporadically with fentanyl in multiple jurisdictions, including Chicago, Philadelphia and Pittsburgh, from mid-2023 to mid-2024, according to the CDC.

From October 2025–January 2026, medetomidine was detected in treated wastewater every week in at least one of 14 states included in a wastewater testing program in the U.S., the CDC said.