Researchers in the US have identified an abnormally slow heart rate, known as ‘bradycardia’, as a symptom of xylazine-opioid overdose. The breakthrough finding could help emergency medical staff detect whether people have been exposed to xylazine, which is increasingly found as an additive in illicit drug supplies.
Around a quarter of the US fentanyl supply is now estimated to include xylazine, a powerful animal sedative. Its use in humans has been associated with severe skin lesions, sedation and hypothermia. ‘Since it’s not authorised for humans, there are knowledge gaps about how xylazine impacts patients,’ the researchers from the Icahn School of Medicine at New York’s Mount Sinai Health Systems state.
The researchers conducted a study of almost 1,300 people with suspected opioid overdoses in US emergency departments between 2020 and 2023, comparing toxicology samples from patients with both xylazine and an illicit opioid in their blood to those with an illicit opioid only. Patients with xylazine-fentanyl overdose were twice as likely to have bradycardia compared to those without xylazine says the study, which is published in the journal Addiction.
Xylazine – known as ‘tranq’ or ‘tranq dope’ in the US, especially when mixed with fentanyl or heroin – was banned as a class c substance in the UK last year, following advice from the ACMD. Researchers from King’s College London (KCL) warned in 2024 that the drug was already present in the UK’s drug market, and was ‘not limited’ to heroin supplies. The KCL collated evidence of xylazine detections from all UK toxicology labs and found the presence of xylazine in 16 people, 11 of which cases were fatalities. The UK’s first xylazine death occurred in May 2022 – a 43-year-old man in the Midlands.
Although a non-opioid, people are still recommended to use naloxone in the event of a xylazine overdose since opioids will usually also be present. While xylazine is commonly mixed with opioids it has also been detected ‘alongside stimulant drugs such as cocaine, and found in items sold as counterfeit codeine and diazepam tablets and even THC vapes’, the KCL report stated.
‘People using opioids do not intentionally seek out substances like xylazine, but are inadvertently exposed to them, and we still don’t know all of the potential health effects that these novel substances might have for patients,’ said assistant professor of emergency medicine at Mount Sinai, Jennifer Love. ‘There’s also no way to test patients at the bedside for xylazine, so doctors in the emergency department have no way of knowing if a patient has been exposed to this drug in addition to fentanyl or other illicit opioids – they require a blood test for detection that’s sent to a specialized toxicology lab.’
Being able to associate a clinical sign, such as a slow heart rate, with xylazine following an overdose could therefore be extremely helpful to doctors, she continued. ‘They can provide harm reduction counselling for patients about adulterants and resources like drug testing strips.’
Meanwhile, addiction warnings on the UK packaging and patient information leaflets for a range of gabapentinoids, benzodiazepines, and ‘z-drugs’ are being strengthened following a safety review, the Medicines & Healthcare products Regulatory Agency (MHRA) has announced. Leaflets will now include clearer definitions of dependence and addiction as well as improved guidance on how to safely taper and stop use, the agency states. There will also be warnings not to use the medicines with opioids or alcohol, and not to share them with other people.
‘Addiction and dependency can happen to anyone taking these medicines, even when used as directed,’ said MHRA chief safety officer Dr Alison Cave. ‘That’s why we are strengthening warnings so patients and healthcare professionals can better understand the risks. These medicines remain valuable treatments for many patients, and it’s important they have the information they need to be able to use them safely.’
Xylazine-opioid overdose study published in the January 13 issue of Addiction