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

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.