Nitazenes are a group of powerful synthetic opioids that were created 50 years ago by Chemische Industrie Basel, a Swiss chemical company as potential pain relief medications. However, they were so potent and their therapeutic window so small, they were never approved as a medicine. These drugs are mu-opioid receptor agonists that produce psychoactive effects comparable to morphine, heroin, and oxycodone.
All nitazenes derive from the chemical structure, 2-benzyl-benzimidazole. In the past few years, several nitazenes have emerged in the illicit recreational drug market. At least 23 variants of nitazenes have been confirmed worldwide. Some of them (isotonitazene, metonitazene, protonitazene, and etonitazene) are up to 40 times more potent than fentanyl and 500 times more potent than heroin. They have already caused hundreds of deaths in Australia, Brazil, most of Europe, the United Kingdom, North America and west Africa.
Nitazenes are available in powders, counterfeit prescription medicines, including fake oxycodone and benzodiazepine pills. They have most frequently been combined with fentanyl but may also be used with benzodiazepines, cocaine, heroin, methamphetamine, and tramadol.
The potency of nitazenes makes them attractive to smugglers because the same number of users can be served with smaller amounts. They are easier and cheaper to distribute for the same price. However, their potency puts users at higher risk of overdosing.
Bellingcat has uncovered more than 1,000 online advertisements for 6 of the most common types of nitazenes. These ads offer worldwide delivery. Many of the accounts were linked to companies in China.
The lethal doses for nitazenes in humans, particularly in combination with other drugs, are not known. Many factors influence overdose-related morbidity and mortality, including not only the drug, but also the amount taken, the route of administration, possible drug-drug interactions or drug-alcohol interactions, body weight, opioid tolerance, and underlying health status.
The emergence of nitazenes creates additional concern as people with substance use disorder seek more potent drugs to satisfy their addiction. Routine illicit drug tests do not detect nitazenes. Physicians treating treating people with drug-induced respiratory depression may not be aware of the presence of nitazenes.
In theory, some nitazenes can be antagonized by the opioid receptor antagonists, such as naloxone and nalmefene, but it is not clear if the high potency and impurities of the nitazenes might limit their effectiveness.
In January 2025, the British government used a generic definition of nitazenes, as compounds derived from the core structure of 2-benzyl-benzimidazole, to categorize all nitazenes as class a drugs, the most severe criminal classification, in the hope of capturing and banning future variations. China implemented a nitazene ban using a similar generic definition in June 2025.
References
Pergolizzi J et al. Old Drugs and New Challenges: A Narrative Review of Nitazenes. Cureus, 2023 Jun; 15(6): e40736. Published online 2023 Jun 21. doi: 10.7759/cureus.40736
The Rise of Nitazenes: Chines Suppliers Behind Ads for Deadly Opioids Targeting Europe, Bellingcat.com, January 20, 2025. https://www.bellingcat.com/news/2025/01/20/chinese-link-to-nitazenes-targeting-europe/
A dangerous new class of synthetic opioid is spreading: Some nitazenes are far more potent than fentanyl. The Economist, September 9, 2025.
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