Medetomidine

The opioid crisis has continued to lead to tens of thousands of deaths per year. The crisis has become increasingly complicated due to the emergence of mixtures of fentanyl and other central nervous system depressants. The recent addition of xylazine, a veterinary sedative, has made overdoses more difficult to reverse.

After public health workers began to educate communities to become more aware of xylazine, overdoses involving a new tranquilizer started to appear. Medetomidine is a nonopioid sedative that is a potent alpha-2-adrenergic receptor agonist. It is a legal, widely used veterinary tranquilizer, but is not approved for use in humans. Medetomidine is 200 to 300 times more potent than xylazine and causes a longer duration of sedation and analgesia. It can cause sedation, bradycardia, reduced cardiac output, hypotension, and decreased respiration. Stopping medetomidine following regular use may lead to severe withdrawal symptoms including hypertension, anxiety, nausea, vomiting and fluctuating alertness.

Medetomidine is commonly referred to as ‘rhino tranq,’ ‘mede,’ or ‘dex’ among people who use illicit opioids. It was first identified in the illegal drug supply in 2021 and began appearing with fentanyl in mid-2023. By late July 2024, it had been detected in drug samples and biospecimens of people who use illicit opioids in at least 18 states and the District Of Columbia. From October 2025 to January 2026, it was detected in treated wastewater every week in at least one of 14 states that participate in a wastewater testing program.

Medetomidine is often combined with xylazine and fentanyl, making overdoses more difficult to reverse. The effects of medetomidine cannot be reversed with naloxone. Combined exposure is often associated with longer periods of sedation and recovery times that sometimes require hospitalization. 

References

Palamar JJ, Krotulski AJ. Medetomidine Infiltrates the US Illicit Opioid Market. JAMA, 2024; 332:1425-26. Published online September 04, 2024. doi:10.1001/jama.2024.15992. 

Nham A, Le JN, Thomas SA, et al. Overdoses Involving Medetomidine Mixed with Opioids — Chicago, Illinois, May 2024. MMWR Morb Mortal Wkly Rep 2025;74:258–265.

CDC Health Alert Network, Medetomidine in the U.S. Illegal Fentanyl Supply Increasing Risk for Overdose and Severe Withdrawal Syndrome, April 2, 2026, CDCHAN-00527.