Veterinary tranquiliser medetomidine shows up in Scottish heroin and US fentanyl with no human antidote
A veterinary sedative called medetomidine has been found in roughly one-fifth of heroin samples in Scotland and in a large share of fentanyl tests in the US, and there is no proven reversal drug for humans.
Developed over 50 years ago as the veterinary tranquiliser Domitor, medetomidine has resurfaced in the illicit drug market, showing up in about one-fifth of heroin samples tested in Scotland and in the majority of fentanyl samples examined in Philadelphia between 2024 and 2025. The drug acts on the same receptors as xylazine but is far more potent, with minute doses capable of raising blood pressure dramatically before a dangerous crash.
Because it depresses the brain's wakefulness centre rather than breathing, standard opioid overdose treatments like naloxone are ineffective, and the animal antidote atipamezole can provoke severe withdrawal reactions in humans. The substance is also being detected in street-sold benzodiazepines across the UK. Experts warn that without a human-safe reversal agent, overdoses pose a growing public-health threat, prompting calls for expanded safe consumption sites such as Glasgow’s The Thistle, broader drug testing, and the UK Advisory Council on the Misuse of Drugs’ recommendation to classify medetomidine as a class-C drug and train emergency responders. The government’s response to these recommendations is still pending.
Why it matters
Medetomidine’s spread in street drugs creates overdose risks that current treatments cannot safely address.
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