Characterizing the Emergence of Medetomidine in Southern California Fentanyl Markets
- 1University of California, Los Angeles
Abstract
BackgroundMedetomidine, a potent sedative, is increasingly present in fentanyl-related hospitalizations and deaths. Multiple states have passed legislation to control xylazine--a pharmacologically similar sedative in the illicit opioid supply. Medetomidine may function as a highly potent substitute for xylazine with significant overdose risk and withdrawal potential. Medetomidine has previously been described mostly in eastern U.S. fentanyl markets. Here, we characterize medetomidine-containing drug samples obtained in Southern California 2023-2026.
MethodsAnonymous participants in Southern California voluntarily provided drug products to a community-based drug checking program. All samples underwent direct-analysis-in-real-time mass spectrometry (DART-MS). A subset was quantified by liquid-chromatography tandem mass spectrometry (LC-MS/MS). A smaller subset underwent enantiomeric analysis. We calculated other compounds co-present with medetomidine, the prevalence of medetomidine in fentanyl over time, the concentration of medetomidine, and the enantiomer makeup of medetomidine.
ResultsThe quarterly prevalence of medetomidine co-present with fentanyl rose from {approx}6 % in May 2025 (month of first detection) to {approx}25 % by August 2026. The average medetomidine concentration was 0.4 % mass fraction. The most common co-detected substances with medetomidine were fentanyl and adulterants such as lidocaine and xylazine. All medetomidine samples that underwent enantiomeric analysis (n = 13) were identified as racemic.
ConclusionMedetomidine represents a rapidly emerging adulterant in the Southern California fentanyl supply. All samples assessed for enantiomer status were racemic medetomidine, suggesting they were not diverted from human pharmaceutical or medical supplies. Given its high potency, a small amount (<1.5%) is likely still a physiologically significant quantity of the drug.
Highlights- Medetomidine is an emerging adulterant in the Southern California fentanyl supply. - The share of fentanyl with medetomidine rose from 6% in May 2025 to 25% in Aug 2026. - Nearly all medetomidine samples were detected in the presence of fentanyl. - Medetomidine was found in two samples of DMT obtained via the dark web. - The mean concentration of medetomidine was 0.4 % mass fraction among 22 cases. - All tested medetomidine was racemic, not diverted dexmedetomidine.
Related
- La présence de médétomidine sur le marché des drogues illicites.
- A sequential dose-finding study of fentanyl during remimazolam induction for tracheal intubation in adults
- A double-blind randomized controlled trial comparing intranasal dexmedetomidine with and without fentanyl for pediatric premedication
- "It Just Puts You Out!" Tranq Sleep, Sensory Discernment, and the Experience of Consuming Xylazine-Adulterated Fentanyl in Rural North Carolina
- Assessment and development of decontamination strategies for fentanyl and fentanyl analogues
BibTeX
@misc{koncsol2026characterizing,
title = {{Characterizing the Emergence of Medetomidine in Southern California Fentanyl Markets}},
author = {A. J. Koncsol and J. R. Friedman and C. A. Molina and M. Grabill and M. E. Godvin and R. Romero and E. A. Samuels and E. Sisco and C. L. Shover},
howpublished = {medRxiv},
year = {2026},
month = oct,
doi = {10.64898/2026.10.13.26365459},
url = {https://www.medrxiv.org/content/10.64898/2026.10.13.26365459v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Characterizing the Emergence of Medetomidine in Southern California Fentanyl Markets
AU - A. J. Koncsol
AU - J. R. Friedman
AU - C. A. Molina
AU - M. Grabill
AU - M. E. Godvin
AU - R. Romero
AU - E. A. Samuels
AU - E. Sisco
AU - C. L. Shover
PY - 2026
DA - 2026/10/13
PB - medRxiv
DO - 10.64898/2026.10.13.26365459
UR - https://www.medrxiv.org/content/10.64898/2026.10.13.26365459v1
AB - BackgroundMedetomidine, a potent sedative, is increasingly present in fentanyl-related hospitalizations and deaths. Multiple states have passed legislation to control xylazine--a pharmacologically similar sedative in the illicit opioid supply. Medetomidine may function as a highly potent substitute for xylazine with significant overdose risk and withdrawal potential. Medetomidine has previously been described mostly in eastern U.S. fentanyl markets. Here, we characterize medetomidine-containing drug samples obtained in Southern California 2023-2026. MethodsAnonymous participants in Southern California voluntarily provided drug products to a community-based drug checking program. All samples underwent direct-analysis-in-real-time mass spectrometry (DART-MS). A subset was quantified by liquid-chromatography tandem mass spectrometry (LC-MS/MS). A smaller subset underwent enantiomeric analysis. We calculated other compounds co-present with medetomidine, the prevalence of medetomidine in fentanyl over time, the concentration of medetomidine, and the enantiomer makeup of medetomidine. ResultsThe quarterly prevalence of medetomidine co-present with fentanyl rose from {approx}6 % in May 2025 (month of first detection) to {approx}25 % by August 2026. The average medetomidine concentration was 0.4 % mass fraction. The most common co-detected substances with medetomidine were fentanyl and adulterants such as lidocaine and xylazine. All medetomidine samples that underwent enantiomeric analysis (n = 13) were identified as racemic. ConclusionMedetomidine represents a rapidly emerging adulterant in the Southern California fentanyl supply. All samples assessed for enantiomer status were racemic medetomidine, suggesting they were not diverted from human pharmaceutical or medical supplies. Given its high potency, a small amount (<1.5%) is likely still a physiologically significant quantity of the drug. Highlights- Medetomidine is an emerging adulterant in the Southern California fentanyl supply. - The share of fentanyl with medetomidine rose from 6% in May 2025 to 25% in Aug 2026. - Nearly all medetomidine samples were detected in the presence of fentanyl. - Medetomidine was found in two samples of DMT obtained via the dark web. - The mean concentration of medetomidine was 0.4 % mass fraction among 22 cases. - All tested medetomidine was racemic, not diverted dexmedetomidine.
ER -