While the dangers of fentanyl have dominated headlines for years, the number of deaths from another class of extremely potent synthetic opioids called “nitazines” has been steadily rising. For decades, knowledge about nitazines – also known as benzimidazole opioids – was limited to researchers in opioid pharmacology. That changed in 2019, when the drugs appeared on the illegal drug market first in Europe and then in the USA.
They started in eight countries and had spread to 19 by 2022. According to the United Nations Office on Drugs and Crime’s World Drug Report 2025, the presence of nitazines in the illicit drug market has been increasing for five years and poses a growing threat to public health. But it is unclear how nitazines entered the global drug supply in the first place, as there was never any public demand for them.
The biggest concern is Nitazin overdoses. That’s partly because isotonitazene – the most common nitazine, also called “ISO” – is five to nine times stronger than fentanyl, which itself is generally 25 to 50 times stronger than heroin, which is about twice as strong as morphine. That means less than 2 mg of ISO — the tip of a pencil or a few grains of sand — can be fatal, says Brian Townsend, retired senior special agent in charge of the Drug Enforcement Administration (DEA) and founder of Only 2mg Inc., a nonprofit that focuses on fentanyl and other new illicit substances.
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Currently, there is limited data on Nitazin deaths in the United States. Next are two studies – but both do not provide accurate estimates of global magnitude and are likely underreporting of nitazine overdoses in the Americas. The first study showed that nitazines played a role in at least 200 overdose deaths in Europe and North America between 2020 and 2021. The second found 93 deaths in 2022 from eight case reports, mostly from the US.
Here’s what you need to know about nitazines, why they’re spreading, and their impact on public health.
What are Nitazines?
Nitazines are a class of potent synthetic opioids that were developed in the 1950s as an alternative to morphine but were never approved for medical use because they carried a high risk of overdose, Townsend says. Fentanyl was developed at the same time.
“They are not related to opioids derived from morphine or fentanyl, but work similarly by binding to opioid receptors and causing effects such as pain relief, euphoria, sedation, respiratory depression, and overdose and death,” says Ryan Marino, MD, a toxicologist and addiction medicine expert at University Hospitals in Cleveland.
Nitazines come in many forms, including pills, powders and sprays – both in “pure” form and mixed with other drugs such as heroin, fentanyl and benzodiazepines. They can be taken intravenously, intranasally, orally, sublingually and by inhalation (vaping).
Nitazines work by binding to opioid receptors and stopping pain or reducing its intensity – just like heroin, fentanyl or other opioids, explains Townsend. “The problem is that they are extremely powerful and slow down the part of the brain that tells you to breathe,” he says. “This causes respiratory depression. We sometimes call this ‘sleepy death’.”
In the US, clonitazene and etonitazene – two types of nitazines – were classified as Schedule 1 drugs in the original Controlled Substances Act of 1971, with high potential for abuse and no accepted medical use. In 2020, the DEA classified isotonitazene as a Schedule 1 substance, and since then seven other nitazines have been similarly classified.
Although they are illegal, enforcement is difficult. “The chemicals that make up Nitazines are relatively inexpensive, easily accessible and cheap to produce, making them more widely available worldwide,” says Jessica Steinman, chief clinical officer at No Matter What Recovery in Los Angeles.
It is also difficult to get exact figures about the extent because nitazines can hardly be reliably detected. “Standard fentanyl test strips do not detect nitazines, and most hospital toxicology panels do not include them – misattributing overdoses and underreporting deaths,” says Jason Bernstein, LMFT, clinical director at Clear Behavioral Health. “This is destabilizing for people with addiction because harm reduction strategies collapse when you can’t test for the most dangerous thing on offer.”
Marino says it’s unclear why nitazines entered the drug supply in the first place – people don’t actively seek them out, and there was never any known demand. “They could be a response to efforts to phase out other opioids or even other drugs like benzodiazepines,” he says. “In almost all cases where Nitazines are found, they are mixed with other drugs, primarily fentanyl, and are not sold as Nitazines.” Between 2019 and 2023, Nitazines were detected in at least 4,300 police drug seizures in the United States.
While we don’t have a complete picture of nitazine deaths, we know they occur across the United States. A 2022 and 2023 study found Nitazine in wastewater samples from Washington and Illinois. The Ohio Department of Health reported seven nitazine-related overdose deaths in 2020, followed by an average of 57 deaths in 2021 and 2022 and 77 in the first six months of 2023.
While there were no nitazine deaths in Tennessee in 2019, there were 92 between 2020 and 2023. Most overdoses also involved fentanyl. Additionally, the Pennsylvania Department of Health reported at least 50 fatal overdoses since 2020, with a record 29 deaths in 2024.
As with other opioids, naloxone can reverse a nitazine overdose. However, multiple doses may be required due to potency.
According to Justin Gurland, a social worker who specializes in addiction, there is no specific population that intentionally seeks Nitazine. “That’s what makes them so dangerous,” he says. “Most people don’t know they’re taking them. Nitazines are mixed into heroin, counterfeit painkillers and even non-opioid drugs, reaching people who never intended to take an opioid.”
Why are nitazines spreading?
Nitazines are becoming increasingly popular because they are cheap, powerful and addictive, says Townsend. “They’re cheap, so drug dealers ‘stretch’ their offerings to make more money,” he explains. “They are powerful, amplifying the high, and many who struggle with addiction seek that stronger high. And they are addictive – repeat customers mean more money for those who mix them.” Because of their potency, “the doses can be very small, making them easier to transport and hide,” says Steinman.
Many experts believe that nitazine analogues entered the recreational market to replace fentanyl analogues after China and the US introduced broad bans on fentanyl analogues, says Marthe M. Vandeputte, a researcher at Ghent University.
On July 1, 2025, China introduced a generic ban targeting Nitazin analogues. “With a single regulation, most of the known Nitazines became illegal in China – and China is the most important production country,” says Vandeputte. “We expect this to have a major impact on the market for new synthetic opioids because fewer new analogues are emerging.” But other classes of synthetic opioids could emerge.
“In addition, the 2022 Taliban ban on opium poppy cultivation could impact heroin supplies in Europe and elsewhere, which could further fuel the rise of synthetic opioids like Nitazine,” she says.
Why are Nitazines so worrisome?
More than 20 different Nitazin variants have emerged since 2019, with new ones appearing all the time. “Once a compound is classified, manufacturers modify the molecule slightly so that it is not yet technically illegal,” says Bernstein. “What started with heroin has expanded to include stimulants, depressants and counterfeit medications. Anyone who buys any street drug today is potentially at risk.”
For Luke Archibald, MD, chief of addiction psychiatry at Dartmouth Hitchcock Medical Center, the many unknowns are concerning – especially because nitazines are made up of chemical groups with potentially different properties, such as varying potency and response to naloxone. “It’s concerning not knowing what might be in a particular shipment, and there are reports of Nitazine in counterfeit pills sold as other substances – taken by people with no opioid experience,” he says.
The potency is also alarming. “Even a trace – a point that fits on the tip of a needle – can slow or stop breathing,” says Gurland. “The difference between a dose and a fatal overdose can be microscopic.”
Gurland says the biggest problem is that most people don’t know they’re taking Nitazines – they show up in counterfeit pills, powders, “oxycodone” imitations, heroin and even non-opioids. “For people living with addiction, this unpredictability makes any use potentially deadly. It’s not just about potency – it’s about invisibility,” he says. “They’re difficult to detect and labs often don’t test for them. That’s why they’re considered the next wave of the synthetic opioid crisis.”
Like fentanyl, nitazines are quickly becoming a public health problem. “This combination of strength and stealth is what makes them so dangerous,” says Gurland. “People don’t know what they’re taking, first responders don’t know what they’re dealing with, and standard drug tests often miss them, spreading an invisible risk into already burdened communities.”