The study characterised medetomidine in drug samples given anonymously to a Southern California drug checking programme from 2023 to 2026. All samples underwent DART-MS, a subset was quantified by LC-MS/MS, and 13 underwent enantiomeric analysis. Medetomidine's quarterly prevalence in fentanyl samples rose from about 6% in May 2025 to about 25% by August 2026. Mean concentration was 0.4% mass fraction, and all 13 tested samples were racemic, an equal mix of both enantiomers. The substances most often detected with medetomidine were fentanyl and the adulterants lidocaine and xylazine. Samples were given voluntarily to one programme, and only 13 underwent enantiomeric analysis.
Why it is interesting: Medetomidine was previously described mostly in eastern US fentanyl markets. All tested samples were racemic, suggesting they were not diverted from human pharmaceutical or medical supplies.
Abstract — the authors' own words, CC BY
Background:
Medetomidine, 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. Methods:
Anonymous 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. Results:
The quarterly prevalence of medetomidine co-present with fentanyl rose from ≈6 % in May 2025 (month of first detection) to ≈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. Conclusion:
Medetomidine 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.
Cite this item
BibTeX
Free sign-up. A digest of the new papers twice a week, grouped by domain.
Other drivers in Behavioural science
-
Diet, exercise and sleep
What people eat and how much they move: what the measured evidence says each does to mortality, and what has been shown to change either.
2 this week -
Smoking and vaping
How far smoking has fallen and how many deaths it still causes, what vaping is doing to the people who take it up, and what generational bans will show.
4 this week -
Alcohol and drug use
What is happening to deaths from alcohol, drugs and suicide, whether they move together, and how much of it is behaviour and how much circumstance.
3 this week -
Social connection
Isolation, loneliness and mortality: what the evidence shows, how far the relationship is causal, and what interventions have shown.
None this week Earlier → -
Infection and pandemics
Infection and pandemics: the risks, and how well prepared we are
8 this week -
Adherence and persistence
Whether a treatment is actually taken, for how long, and what changes either.
2 this week
