St. Louis County health officials are sounding the alarm after a veterinary sedative known on the street as "rhino tranq" turned up in local street drugs, with at least some samples tied to the Berkeley area. At a Thursday briefing, county public-health director Dr. Kanika Cunningham held up a naloxone (Narcan) dispenser as she urged residents and first responders to treat every suspected overdose as a medical emergency. Health staff warned that the drug’s powerful sedative effects can linger even after naloxone is given and may require prolonged monitoring and respiratory support. County teams say they are ramping up surveillance of the local drug supply and are reminding people who use drugs, along with their loved ones, to carry naloxone and call 911 for any suspected overdose.
Local alert
The discovery was first reported by the St. Louis Post-Dispatch, which notes that county health staff identified medetomidine, often called "rhino tranq," in drug samples linked to Berkeley. The paper published a photo of Dr. Cunningham with a Narcan dispenser as officials warned that the newly detected sedative complicates how overdoses are handled.
What 'rhino tranq' does
Medetomidine is a veterinary sedative similar to xylazine but markedly more potent, and it is increasingly showing up as an adulterant in fentanyl supplies. In a public release, the Southern Nevada Health District warned that the drug can cause prolonged unconsciousness, a slow heart rate and low blood pressure. The agency also noted that because medetomidine is not an opioid, naloxone will not reverse its direct sedative effects, even though naloxone should still be given to counter any opioid that may be present.
Clinical alarms from Philadelphia
Clinicians in other cities have already seen how bad things can get when medetomidine enters the local drug supply. A CDC "Notes from the Field" report described 165 patients admitted across three Philadelphia health systems with suspected medetomidine-related withdrawal or prolonged sedation between September 2024 and January 2025. Those hospitalizations often required intensive monitoring and, in some cases, mechanical ventilation, an experience public-health experts say shows why the drug is a serious emerging threat.
How to respond
Public-health guidance is blunt about what to do if you find someone unresponsive: give naloxone immediately, begin rescue breathing and call 911. The Southern Nevada release and federal guidance both stress that naloxone should be used for any suspected opioid overdose even though it may not reverse the effects of non-opioid sedatives. Rescuers should prioritize airway and breathing support while waiting for emergency responders. Clinicians treating suspected medetomidine exposure are advised to provide supportive care and to consult local hospital protocols and public-health alerts for updated treatment guidance.
St. Louis County's public-health team says it will keep testing and sharing information with hospitals and community partners as the situation evolves. For national and clinical background on medetomidine, see guidance from the Philadelphia Department of Public Health and the Centers for Disease Control and Prevention.
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