Medetomidine in Chicago's Opioid Supply: The Largest Overdose Cluster Yet, May 2024

At a glance

• Known before: medetomidine, a nonopioid sedative not approved for use in people, has turned up in illegally made opioids across North America since 2022.
• Found here: during May 11–17, 2024, Chicago had 12 confirmed and 26 probable medetomidine-involved overdoses, mostly in non-Hispanic Black or African American men aged 45–64. The telltale signs were a slow heart rate (bradycardia) and poor response to naloxone. Fentanyl was in every blood specimen and drug sample that held medetomidine.
• What follows: surveillance across sectors is needed to spot new adulterants fast. Clinicians who see unusual overdose symptoms should call their local health department — and keep giving naloxone and linking people to treatment.

The alert

On May 11, 2024, the Overdose Detection Mapping Application Program alerted the Chicago Department of Public Health (CDPH) and the Illinois Department of Public Health (IDPH): 50 emergency medical services (EMS) responses for suspected opioid overdoses that day, more than two standard deviations above the 2023 daily average of 27.4 — mostly on Chicago's West Side. Hospitals and the Illinois Poison Center also reported patients with bradycardia whose overdose symptoms naloxone didn't fully reverse.

Powders carried by five patients in the emergency department held medetomidine mixed with fentanyl, in varying amounts. It was the drug's first detection in Chicago. Medetomidine depresses the central nervous system and may be more potent than xylazine, another sedative that had recently entered the drug supply.

How it was investigated

On May 17, CDPH asked CDC for help. The team used:

1. blood specimens and drug samples tested through the Drug Enforcement Administration's toxicology program (at the University of California, San Francisco) and the Center for Forensic Science Research and Education, with help from the Chicago Recovery Alliance;
2. Cook County medical examiner death records;
3. Chicago Fire Department EMS records;
4. records from the three West Side emergency departments that received the most of these patients.

How cases were identified, May 11–17, 2024. CDC, MMWR.

What was found

Of 181 patients treated for suspected opioid overdose at the three hospitals, 12 were confirmed, 26 probable and 140 suspected; three were ruled out.

• Tests: 12 of 15 blood specimens held medetomidine, all alongside diphenhydramine and fentanyl, and often quinine, a cocaine metabolite, morphine, xylazine or bromazolam. Five of 10 drug samples held medetomidine and fentanyl, adding two probable cases; the other 24 probable cases came from clinical signs.
• Who: of the 38 confirmed and probable cases, 84% were male, 87% non-Hispanic Black or African American, and 63% aged 45–64. 18 (47%) said they meant to use heroin; snorting was the most common route reported (eight), though for most this was unknown.

• Naloxone: 11 of the 12 confirmed patients (92%) improved only partly or not at all. The one who fully recovered had the lowest medetomidine level; levels ranged from 0.7 to 63.7 ng/mL.
• Care: five needed atropine for slow heart rate; 16 were admitted, nine to intensive care; 16 needed breathing support and five intubation.
• Deaths: one death was classed as a suspected medetomidine case, but without toxicology it couldn't be definitively linked.

Medetomidine cases and daily EMS responses for suspected opioid overdoses, Chicago, May 8–20, 2024. CDC, MMWR.

The response

• Health alerts: CDPH warned of the surge on May 14 and, once medetomidine was found, again on May 20, asking clinicians to report unusual overdoses to the poison center, report clusters, and seek toxicology testing; IDPH took the alert statewide on May 21.
• Drug checking: CDPH and partners promoted community point-of-care drug checking and monthly reporting where overdose transports were highest.
• Treatment: it advised the busiest emergency departments on starting medications for opioid use disorder before discharge and linking patients to care.

What it means

This is the first description of a cluster of medetomidine-involved overdoses — and the largest of confirmed cases yet. Hospitals' thorough testing, their reports to the poison center, and fast testing of samples and specimens pinned it down. Since 2023, CDC has supported testing of drug samples or paraphernalia in 18 local jurisdictions, Chicago included.

• Bradycardia, usually stronger with medetomidine than with opioids, may help tell these overdoses apart; very high blood pressure also appeared. Heart and breathing support are central to treatment.
• Medetomidine narrows blood vessels in animals; whether it worsens the skin wounds tied to xylazine in people is unclear.
• Naloxone still matters: every sample with medetomidine also held opioids, which naloxone reverses — though it can't reverse medetomidine, and atipamezole, the antidote for medetomidine and dexmedetomidine, isn't approved for people.
• Clinicians facing unusual overdose symptoms should give naloxone and supportive care, contact the health department readily, especially about clusters, and use poison centers for guidance and testing — while continuing opioid use disorder treatment, linkage to care and harm reduction.

Limitations

• Suspected cases may be overcounted: with little known about medetomidine in people, there's no clear set of symptoms, so the investigators favored catching every possible case.
• Confirmed cases may be undercounted: most patients weren't tested, and medetomidine isn't in standard urine drug screens.
• Only three hospitals were included, so others may have seen cases, and results may not apply elsewhere.
• Only May 11–17 was studied. No further clusters have been found in Chicago, but later drug samples have held medetomidine.

For public health

The mix of adulterants in illegal drugs keeps changing: xylazine has already been tied to a worrying rise in deaths, and medetomidine complicates the opioid crisis further. Clinicians and people who use drugs should know it can be in the supply. If someone might be overdosing, give naloxone or another opioid overdose reversal medication, and connect people at risk to evidence-based treatment, services and support.

Sources

Based on "Overdoses Involving Medetomidine Mixed with Opioids — Chicago, Illinois, May 2024," by Amy Nham, John N. Le and colleagues of CDC, the Chicago and Illinois health departments, the Illinois Poison Center, the Drug Enforcement Administration, and partner laboratories and hospitals, Morbidity and Mortality Weekly Report, CDC; a work of the United States government in the public domain.