Disappearing nitazenes: How a lethal synthetic opioid is slipping through post-mortem tests

As Tower Hamlets grapples with one of London’s highest opiate usage rates, a hidden wave of nitazene-linked deaths is going uncounted due to a deadly flaw in post-mortem testing.

A new class of dangerous synthetic opioids called nitazenes was linked to 179 deaths in a span of just a year (2023-2024), according to the Office for Health Improvement & Disparities. 

However, a shocking new study from King’s College London has found that the real number of nitazene-linked deaths could be much higher than previously thought. 

Nitazenes are up to 500 times more potent than heroin, and the amount needed to overdose can be so small it’s not visible to the human eye. Nitazenes are a class of drugs, with many different varieties, all of which have different properties. 

They are hidden in everything from heroin to fake medicines and party drugs. This is of particular concern in Tower Hamlets, where opiate usage is one of the highest in London. 

To determine whether or not nitazenes are a factor in a death, coroners need to test blood samples from the deceased. Nitazenes began posing a serious risk in the UK after the heroin supply was reduced in 2020. Detecting these new opioids in blood has posed a challenge for coroners and toxicologists. 

Rob Moore is a toxicologist and co-host of The Tox Lab podcast. As part of his work, Moore and his colleagues analyse available data on the UK’s drug supply to try to predict what new drugs are emerging. He told the Slice that nitazenes are particularly difficult to detect in blood, partly because of how small they are. 

‘Bear in mind we’re measuring drugs in blood samples, which are highly complicated anyway,’ Moore said, ‘within a blood sample, there are thousands of compounds. 

Actually trying to pick through it all and work out whether one of them might be an opioid is next to impossible, unless you know what you need to look for in that data set.’

Around late 2022 and early 2023, Moore and his colleagues noticed nitazenes appearing much more regularly in the UK drug supply. ‘It was a bit of a challenge, suddenly upscaling […] to actually bring this testing more routinely online,’ he said, ‘certainly a hairy couple of months.’

Nitazene blood testing has since been successfully developed. To Moore’s knowledge, most coroners in the UK can and do test for nitazenes, although it is at the discretion of individual coroners. 

However, one day Moore was performing routine tests on a cadaver and noticed something out of the ordinary. ‘Two cases came into our lab, and it was an unusual situation where they took two sets of blood,’ Moore explained. ‘They took blood when the individual came into the mortuary on day one, and then a post-mortem was carried out a week later, and they took a second set of blood.’ 

‘I detected nitazenes in the first one, but when I […] used the second sample from six days later, the nitazenes had gone.’ 

A BBC Radio 4 Documentary called ‘The Drug Death Detectives,’ follows Moore and his colleagues as they attempt to tackle the nitazene death crisis. Moore described the phenomenon he’d noticed to Dr Caroline Copeland, a Senior Lecturer in Pharmacology & Toxicology at King’s College London, and the Director of the National Programme on Substance Use Mortality (NPSUM). 

Copeland, who tracks drug deaths in the UK, has previously told the Slice that recorded nitazene deaths could be ‘the tip of the iceberg.’ Following anecdotal evidence from toxicologists like Moore that nitazenes had been disappearing from testing, she conducted laboratory testing on mice to see whether a variety of nitazenes were breaking down in the blood. 

The mice were given enough nitazenes to cause an overdose and then refrigerated for a week, in the same way a human body would be refrigerated before testing in a mortuary. Speaking to the BBC, Copeland said that the study had ‘unfortunately confirmed what we anticipated, all the nitazenes we tested are degrading in the blood.’ 

On average, 89% of the nitazene was degraded, meaning that in smaller amounts, the nitazene in the blood could fall below the limits of detection. In some cases, the nitazenes had become completely undetectable. 

‘If someone only has a small amount, and only 89% of it is gone, it may have fallen below the limit of detection.’ Copeland’s study is currently being peer-reviewed and has not yet been released. 

A separate study published in the Journal of Analytic Toxicology focuses on nitro-nitazenes and has confirmed that they degrade in post-mortem blood samples. Forensic toxicologist Claire Parks, an author on the nitro-nitazenes study, said:  ‘The toxicology community can, and have, put processes in place to help us identify cases where nitazenes have been taken but may have broken down/degraded.

We now know to look for nitazenes in post-mortem blood samples that have had preservatives added (this helps stop the degradation of nitazenes in the post-mortem blood sample), and we can also use modern analytical techniques that can identify the degradation products of nitazenes. This allows us to confirm nitazene use even in cases where the parent nitazene has degraded.’

Although toxicology is innovating in order to detect nitazenes, coroners testing suspected opioid overdose deaths on a day-to-day basis have been subject to budget and time limitations, and are not always able to use the most sophisticated possible techniques for detection.

Professor of Pharmacology Graeme Henderson from the University of Bristol explained to the Slice that ‘Until recently when coroners have a drug death and they think it involves heroin or methadone, they may just have asked the forensic lab to test for heroin, morphine and methadone. So if they get a positive result then it just goes in as a heroin/morphine/methadone death.’ Similarly, a lab may choose to only test for fentanyl and not nitazenes, or test for nitazenes without the innovations described by Parks.

In short, nitazenes are degrading in blood and becoming undetectable in post-mortem examinations. This has major implications for what we know about nitazene deaths – the 179 deaths detected in 2023/2024 could be a fraction of the actual fatalities. Copeland told the BBC, ‘Whatever the number is that we’ve counted, I think we’re undercounting.’ A range of improvements to nitazene testing are being introduced across the country outside of post-mortem toxicology, including testing the urine samples of people in drug treatment.

Whatever the number is that we’ve counted, I think we’re undercounting.

Dr. Caroline copeland

In addition to challenges with testing, nitazenes are difficult to track because of how many different derivatives there are. New versions of nitazenes continue to emerge, each with slightly different structures and properties. 

Henderson explained that this is largely due to market and legal pressures. Once a certain way of creating a synthetic opioid becomes popular, governments will attempt to restrict its formula and/or its precursors, e.g. the chemical ‘ingredients’ used to create it. ‘So you just get different [pecursors] and you end up with a compound that’s slightly different shape,’ Henderson said. 

Alternatively, he explained that drug dealers may try to make a variation on a synthetic opioid because that particular formula is not yet illegal. ‘Sometimes in the way [governments have] constructed their laws, you have to name the specific drug to make it illegal,’ Henderson said, ‘So one of the reasons why we have all these variants is to try to get around the law.’ Currently, the UK government is in the process of attempting to ban nitazenes under a generic definition, which would spatially remove the incentive for dealers to make new derivatives.

Thomas Lonsdale, a Pharmacology Ph.d. student specialising in nitazenes, told the Slice that ‘Over the past maybe five, six years, there’s been an explosion in terms of the number of derivatives [of nitazenes].’ 

On a positive note, Moore emphasised that information sharing across different drug monitoring bodies, such as the Office for Health Improvement & Disparities (OHID) and the Welsh Emerging Drugs & Identification of Novel Substances Project (WEDINOS), and NPSUM (Copeland’s database) had made the development of testing easier.

‘This is probably the most engaged we’ve ever been in terms of working with our colleagues,’ he said. This unprecedented collaboration across fields is excellent progress, but also highlights how serious a threat nitazenes and synthetic opioids are currently posing. 

This is probably the most engaged we’ve ever been in terms of working with our colleagues.

Toxicologist rob moore

In Tower Hamlets, the data on nitazene deaths is not shared with NPSUM, meaning it is unknown how many deaths are associated with nitazenes locally. This is because sharing this data is at the discretion of the coroner, who has chosen not to. The Slice reached out for comment on whether or not our coroner is currently testing for nitazenes. We also asked why data is not being shared with NPSUM. However, at the time of publishing, we have not heard back. 

In 2024-25, an estimated 1,190 people were in treatment for opioid use in Tower Hamlets. However, most of the borough’s opioid users are not in treatment at all. So far in this investigation, local rough sleepers have reported serious concerns about synthetic nitazenes. Last week, we also showed how easy it is for nitazenes to enter local drug supplies through the dark web.

Without data on drug deaths from the coroner, Council strategies to address this public health crisis will be delayed. The Tower Hamlets Substance Misuse Strategy does mention nitazenes briefly. However, it is mostly local grassroots groups, like Release, Coffee Afrik and Safe Only CIC, that are doing the work of informing users that their drugs may be laced with dangerous synthetic opioids. 

Without more clarity on drug-death data, it’s hard to tell how many people are dying from nitazene overdoses in east London. Given Tower Hamlets’ high number of opioid users, there is not only an imperative for the Council to act, but an opportunity to provide an example to other boroughs, improving the outcome for the country as a whole.

Read the first instalment of our investigative series on Nitazenes: The arrival of an invisible killer: Is Tower Hamlets ready for Nitazenes?