Professor of Pharmacology Paul Chazot explains how a deadly drug started circulating in the US illicit drug market, and what makes it so dangerous.
The opioid crisis, increasingly driven by synthetic opioids, continues to claim tens of thousands of lives annually in the US alone. Similar crises have arisen all over the western world.
The crisis has become more complex as powerful synthetic opioids like fentanyl, nitazenes and oxycodone are now being “cut” (mixed) with other drugs that slow brain activity, including animal tranquillisers.
The emergence of medetomidine as a new contaminant in the US illicit drug market signals a worrying development in this escalating crisis. When public health officials in Philadelphia first began testing for the drug in May last year, medetomidine was found in 29% of fentanyl samples analysed. Six months later, the drug was found in 87% of fentanyl samples.
Medetomidine, a drug approved only for veterinary use as a sedative and painkiller, has increasingly been implicated in illicit fentanyl-related overdoses.
Like xylazine – another veterinary tranquilliser recently detected in street drugs – it is believed that medetomidine is added to fentanyl to boost its euphoric effects and hence make it more appealing to users. However, medetomidine is even more potent and longer-lasting than xylazine.
An overdose of medetomidine can cause extreme sleepiness, very low blood pressure, slow heart rate, trouble breathing (respiratory failure), and even coma or death. This is because medetomidine rapidly depresses the central nervous system and slows the heart rate significantly.
When medetomidine is used with opioids, the risk is even greater because both drugs can slow breathing, and together they can make it much worse.
Police and paramedics use naloxone to reverse fentanyl overdoses. But if the drug is mixed with medetomidine, naloxone won’t work because medetomidine affects the body in a different way.
Atipamezole can reverse the effects of medetomidine – such as sedation, slowed breathing and slowed heart rate – but it’s only been tested in dogs. The US Food and Drug Administration has not approved the drug for human use.
Overdoses from fentanyl and high-potency nitazenes are also common in the UK and across Europe. The spread of medetomidine in street drugs in other parts of the world needs urgent attention.
The first death in the UK involving xylazine was reported by the National Programme on Substance Abuse Deaths in December 2022. Between April 2023 and January 2024, 17 cases were reported in the UK, in a range of opioid tablets and powders, including codeine, tramadol and heroin.
So far, no confirmed cases involving medetomidine have been reported in the UK. If trends in the US are reliable indicators, the UK may face similar challenges soon.
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