European governments have claimed that the Russian state killed the imprisoned opposition politician Alexei Navalny in 2024 with an obscure toxin called epibatidine. Speaking at a security conference in Munich, the UK’s foreign secretary Yvette Cooper said that only the Russian government ‘had the means, motive and opportunity to deploy this lethal toxin against Alexei Navalny during his imprisonment in Russia’.
Following the announcement, representatives of the UK, Sweden, France, Germany and the Netherlands have written to the director general of the Organisation for the Prohibition of Chemical Weapons (OPCW) stating that Russia is in breach of the Chemical Weapons Convention. So what is epibatidine and why has it been linked to Navalny’s death?
What is epibatidine?
Epibatidine is an alkaloid and a potent neurotoxin found in the skin of certain small frogs found in South America. The molecule consists of a chlorinated pyridine ring bound to an azabicyclic structure featuring a protonated amine group.
Isolated in the 1970s, its discoverer initially struggled to accept the surprising presence of chlorine in an amphibian alkaloid. Its molecular formula is C11 H13 N2 Cl.
What makes it toxic?
Epibatidine binds the nicotinic acetylcholine receptors in the body. These are ion channels present on cells in many parts of the body, important for sending messages via nerves and controlling muscle contraction. When the receptors are bound by the neurotransmitter acetylcholine, sodium ions enter the cell and nerve cells fire. However, epibatidine binds to these structures very tightly, overstimulating receptors throughout the body. This causes muscles to spasm, the heart to race and blood pressure to spike. A lethal dose would interfere with muscle contraction enough to cause severe heart problems, breathing paralysis, seizures and, ultimately, death.
In 2017, a team led by researchers at the University of Texas at Austin, US, revealed that frogs that secrete epibatidine have evolved slight mutations in their nicotinic acetylcholine receptors that specifically resist the toxin while still allowing acetylcholine to bind.
Epibatidine’s properties also make it a powerful analgesic, around 200 times more potent than morphine. Because its mechanism differs from that of opioid drugs, research interest grew in the 1990s into whether the molecule or others derived from it could work as non-addictive painkillers. However, enthusiasm has cooled due to the compounds’ unwanted side effects. For example, Abbott Laboratories progressed an analogue (tebanicline) to clinical trial for neuropathic pain but lost interest due to side effects that included nausea, dizziness, vomiting, abnormal dreams and fatigue.
Why do European governments believe it was used to kill Navalny?
Chemical analysis of samples from Navalny’s body smuggled out of Russia led the UK, Sweden, France, Germany and the Netherlands to conclude that the Russian state used the amphibian toxin to poison Navalny. In a joint statement, the governments said that their tests ‘have conclusively confirmed the presence of epibatidine’ in the samples.
The Russian embassy in London released a statement denying the claims, asking ‘what kind of person would believe this nonsense about a frog?’ It said western governments were disrespecting Navalny and engaging in ‘necro-propaganda’. Navalny’s widow, Yulia Navalnaya, has said on social media that ‘now there is proof’ that her husband was murdered, as she had first claimed in September 2025.
It is the latest in a series of cases in which Russia has been accused of using rare and obscure poisons to kill political dissidents. In 2006, Alexander Litvinenko ingested a fatal dose of polonium-210, which investigators concluded was put in his tea by former KGB agents. And in 2018, a rare Novichok nerve agent was used to attack the former Russian intelligence officer Sergei Skripal and his daughter Yulia.
Navalny was also poisoned with a Novichok agent in August 2020, leading him to be hospitalised in a Berlin hospital for several weeks. Western allies believe that Russia maintains an interest in chemical weapons.
Would the use of epibatidine break international rules on chemical weapons?
An attack using epibatidine would breach two international treaties. To use a chemical substance to deliberately harm or kill someone contravenes Article II of the Chemical Weapons Convention. The frog toxin is also covered by the 1972 Biological and Toxin Weapons Convention. Russia is a signatory of both.
While the OPCW can, in theory, perform independent analysis, the results of any tests run on the samples that are currently in the possession of European governments would likely be contested by the Russian government. There are no sanctions available under either of the conventions.
With input from Alastair Hay, toxicologist and emeritus professor at the University of Leeds, and Rebecca Tarvin, a biologist at the University of Berkeley who investigates frog toxins including epibatidine.
No comments yet