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

Introduction: 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.

Methods: 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.

Results: 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).

Discussion And Conclusions: 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.