Deaths due to synthetic opioids nitazenes have likely been underestimated by up to a third.
King's College London research, published today in Clinical Toxicology, sheds light on the UK's growing synthetic opioid problem.
The presence of nitazenes on the unregulated drug market has risen steeply in the last seven years - prompting UK and international bodies to issue public health warnings about their use.
Nitazenes are a class of synthetic opioids which can have potencies of up to 500 times that of heroin. They can be readily manufactured at low cost. These potent synthetic opioids were originally synthesised for use in humans as analgesics but their development was halted due to extreme potencies.
While the National Crime Agency (NCA) reported 333 fatalities linked to nitazenes in 2024, researchers believe that the number of deaths has been underreported as concerns have been raised by toxicologists regarding their stability in postmortem blood samples. This means they are likely being missed by postmortem toxicology tests.
Testing this theory, researchers used anesthetised animal models to find that on average only 14% of nitazene present at the time of overdose was present when tested under real-world pathology and toxicology sample handling conditions.
The team then used modelling to reveal a 33% excess in drug deaths in Birmingham in 2023, using data from the UK National Programme on Substance Use Mortality (NPSUM) based at King's College London. They believe that a credible explanation for at least some of these excess deaths may be due to the non-detection of nitazene that degraded prior to toxicology testing being performed. It typically takes around a month for blood samples to be analysed by toxicologists.
Dr Caroline Copeland, Senior Lecturer in Pharmacology & Toxicology at King's College London, said: "If nitazenes are degrading in post-mortem blood samples, then we are almost certainly undercounting the true number of deaths that they are causing. That means we're trying to tackle a crisis using incomplete data. When we don't measure a problem properly, we don't design the right interventions - and the inevitable consequence is that preventable deaths will continue."
Understanding how nitazenes degrade, and what they degrade into, is critical. If we can identify these breakdown products and where degradation is occurring, we will be able to detect deaths more accurately and respond more effectively. Better science leads to better surveillance, and better surveillance will save lives.
Dr Caroline Copeland
"This research shows that the harm caused by nitazenes is likely being significantly underestimated. Because these drugs degrade in post-mortem blood, we may be missing up to a third of the deaths they are involved in, meaning public health responses are being designed and funded for only two-thirds of the real problem.
"Behind this undercount are people dying suddenly from extremely potent opioids, families left without answers, and communities facing a growing but largely hidden toll."
The study also included researchers from University College London, University of Bristol, London School of Hygiene & Tropical Medicine, University of Glasgow, University Hospitals Birmingham NHS Foundation Trust, and King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia.
Animals were anaesthetised throughout the study and received intravenous nitazene injection. Animal studies were performed at University College London following UK Home Office guidelines under the Animals (Scientific Procedures) Act 1986 (PP6856925) and local ethics committee approval.
