“Rhino Tranq” in Connecticut—Prevalence of Medetomidine in the Fentanyl Supply Varies by Data Source

Background: Medetomidine, a veterinary sedative, has emerged as an adulterant in the unregulated fentanyl supply. Exposure may cause profound sedation and a severe withdrawal syndrome. We aimed to better estimate medetomidine prevalence by integrating multiple statewide datasets from Connecticut. Methods: We analyzed 4 datasets from 2025: (a) accidental overdose fatalities, (b) drug seizure testing, (c) driving under the influence (DUI) toxicology, and (d) community-based drug checking using medetomidine test strips (MTS) and field-based Fourier-transform infrared spectroscopy (FTIR). Analyses were restricted to fentanyl-involved cases/samples, and medetomidine prevalence was calculated for each source. Results: Among 579 fentanyl-involved overdose fatalities, medetomidine was detected in 1.4%—though confirmatory testing was limited. Of 259 fentanyl seizure units tested, 41.7% contained medetomidine. Among 177 fentanyl-involved DUI cases, 24.9% were positive for medetomidine on toxicology. There were 169 samples of fentanyl/heroin/dope submitted to community-based drug checking programs that subsequently tested positive for fentanyl and assessed for medetomidine: MTS yielded positive results in 46.2% of samples on average, while FTIR detected medetomidine in 28.4% of samples. Conclusions: This study not only demonstrated that medetomidine is prevalent in the street-based fentanyl supply, but that the prevalence varied by data source. The findings highlight that surveillance mechanisms that rely exclusively on a single data source (typically overdose toxicology data) may misrepresent the true presence of medetomidine in the street supply.