Emergence of Medetomidine in the Unregulated Drug Supply and Its Association With Hallucinogenic Effects.

Medetomidine, a veterinary tranquilizer more potent than xylazine, has emerged as an adulterant in the U.S. illicit fentanyl supply. Analysis of 11,363 drug samples from a national mail-based drug checking program between December 2022 and April 2025 found medetomidine in 2.4% of samples, with growth beginning June 2024. It commonly appeared with fentanyl (58.8%) and xylazine (55.9%). Samples where medetomidine was the primary ingredient were nearly 12 times more likely to be associated with reported hallucinations (17.6%) compared to all other samples (1.2%). These unexpected hallucinations may serve as a signal for medetomidine's presence in local drug markets, contradicting its clinical use for preventing delirium.

Study at a glance

Abstract

The unregulated drug supply in the United States is rapidly evolving, and veterinary tranquillisers have emerged as adulterants of concern, especially in illicitly-manufactured fentanyl. Following the proliferation of xylazine, medetomidine, a more potent sedative, has recently appeared in multiple US states. This study describes the characteristics of medetomidine samples from a national mail-based drug checking program and aims to determine whether medetomidine is associated with hallucinogenic effects. We conducted a retrospective analysis of 11,363 drug samples between December 2022 and April 2025. Samples were sent voluntarily by people who use drugs. Participant-reported sensations and sample characteristics (e.g., colour, texture) were gathered at point-of-contact. Composition was analysed using gas-chromatography mass spectrometry. We estimated adjusted prevalence ratios for hallucinations in medetomidine-containing samples using generalised estimating equations. Medetomidine was identified in 278 samples (2.4%), with pronounced growth beginning June 2024. Medetomidine commonly appeared with fentanyl (58.8%) and/or xylazine (55.9%). Most samples were powders (85.3%). Among all 11,363 samples, those containing medetomidine in primary abundance (n = 136) were more likely to be associated with reported hallucinations (17.6%) compared to all other samples (1.2%; adjusted prevalence ratio: 11.95, 95% confidence interval 6.36, 22.44). Medetomidine is an emerging adulterant, although its risk profile is under-described. Our findings suggest medetomidine may cause hallucinogenic effects, contradicting clinical use for preventing delirium in postsurgical settings. Unexpected hallucinations may serve as a sentinel signal for medetomidine's presence in local drug markets. Education is needed for people who use drugs and clinicians about novel adverse effects of medetomidine.