A sedative developed for cats and dogs is turning up in Scotland’s illicit drug supply. Medetomidine has been found in a fifth of heroin samples in Scotland, and there is no proven antidote if someone overdoses.
Author
- Colin Davidson
Professor of Neuropharmacology, University of Lancashire
Often called a new street drug, medetomidine was actually first developed as a sedative more than 50 years ago. It was patented in 1981 and introduced in Europe in 1987 under the name Domitor – a sedative for use in veterinary medicine.
Its street name, “rhino tranq” , is misleading. There’s no real evidence it has ever been used to sedate rhinos. (Actual rhino tranquilliser is an opioid called etorphine , which is over 1,000 times stronger than morphine.)
Medetomidine is closely related to xylazine, another veterinary sedative that has turned up in illicit drugs in the US and UK. Both act on the same type of receptors in the body and can narrow blood vessels. This has raised concerns that it could cause the severe skin wounds associated with xylazine , although such wounds have not yet been consistently reported with medetomidine.
Medetomidine also acts differently from opioids. It reduces activity in a part of the brain involved in wakefulness – called the locus coeruleus – while opioids can suppress the brain’s control of breathing. Taking them together can therefore produce multiple potentially dangerous effects at once.
Despite working in the same way as xylazine, medetomidine is far more potent. As little as a hundredth of the dose can have the same effect . That makes even tiny amounts dangerous. It can send blood pressure soaring and slow the heart rate right down, sometimes followed by a second wave in which blood pressure crashes.
Despite this dangerous profile, medetomidine keeps turning up in illicit drugs across North America and the UK, usually mixed with other street drugs rather than sold on its own. It’s now been found in about 20% of Scottish heroin samples (tested between April and July), and it appears regularly in street benzodiazepines (“benzos”) sold in the UK.
The picture is worse in the US: between 2024 and 2025, an estimated 83% of fentanyl samples tested in Philadelphia contained medetomidine.
Opioid overdoses can usually be reversed with a drug called naloxone. Unfortunately, there’s no equivalent drug to treat a medetomidine overdose in people.
Vets have one. A drug called atipamezole reverses medetomidine’s effects in animals. But reversing it too fast in humans can trigger a dangerous withdrawal reaction – vomiting, a racing heart and a spike in blood pressure . There is no safe, proven treatment for a medetomidine overdose in humans.
Where the drug is coming from is also murkier than with xylazine, which is thought to come mainly from China. In the US, medetomidine is possibly being illegally diverted from veterinary supplies or manufactured illegally .
What can be done?
Safe drug consumption spaces may help. Glasgow already has one – The Thistle – where people can use drugs with clean needles and healthcare staff on hand. More of these are needed across Scotland.
Knowing exactly what’s been taken matters too. Test strips exist for xylazine, but not yet for medetomidine. Testing blood or urine in a lab is currently the only reliable way to know, and that knowledge could shape how someone is treated.
Raising awareness matters just as much among people who use drugs and among first responders like police and ambulance crews, who need to recognise what they might be dealing with.
Longer-term, what’s really needed is a safe reversal drug; one that can counter medetomidine and xylazine without triggering the dangerous rebound effects seen with existing options.
In October 2025, the UK’s Advisory Council on the Misuse of Drugs made three recommendations : classify medetomidine as a class C drug, like xylazine; train emergency responders on its effects and update public information sites like Talk to Frank; and get border-control labs routinely testing seized drugs for it. The government’s response is pending.
