If Someone Stays Under After Naloxone, the Supply Changed. Medetomidine Is Why.

Someone has just been given naloxone. The breathing has come back, but they are still deeply asleep, heart slow, blood pressure low, and they stay that way. That is exactly the picture the CDC’s April health advisory tells clinicians to consider medetomidine for: an opioid overdose with prolonged sedation that does not respond to the overdose-reversal drug.

A person who stays under after naloxone is not a failed rescue. It is a sign the supply has changed.

Medetomidine is a veterinary sedative not approved for people. The White House drug policy office reported detections climbing from 247 in 2023 to 8,233 in 2025. In its mid-year report, Aegis Sciences, a toxicology lab, cited data from the Center for Forensic Science Research and Education showing medetomidine in 84% of fentanyl samples in the first quarter of 2026, up from 0% in early 2024, while xylazine fell from 97% to 19%. Aegis’s own line is blunt: “neither xylazine nor medetomidine responds to naloxone administration.” Read the sample numbers with their limits: this is forensic and lab testing of drugs that were seized or tested, not a census of every pill and powder on every street, and the Northeast has seen the highest detections. Arizona may differ. Nobody should assume it does.

The second half of the problem comes when someone tries to stop. The CDC advisory lists withdrawal symptoms of racing heart, severe high blood pressure, shifting alertness, tremor, chest pain and vomiting that will not quit. That is easy to mistake for a heart attack or a psychiatric crisis. Mississippi’s health department noted in its own alert that medetomidine is not scheduled under federal law and is not included in standard toxicology testing, so a hospital that does not know to look may not find it.

Here is what is still yours. Naloxone still reverses the fentanyl in the mix, so keep carrying it and use it. If a person stays under afterward, call 911, keep them on their side and keep checking their breathing until paramedics take over, and tell responders what you gave them and when. If you are a clinician, put “prolonged sedation after naloxone” on your triage prompts this week, save your poison center’s number (1-800-222-1222) where your team can find it, and ask whether your emergency department’s withdrawal protocols assume opioids only.

The rescue is not over when the naloxone wears off. It is over when someone trained takes the person’s hand.