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14 February 2026, 15:54 | Updated: 14 February 2026, 16:37
The Russian state has long been accused of using exotic poisons to murder its opponents – whether the nerve agent Novichok or radioactive plutonium isotopes. Could Alexei Navalny have been killed by the toxin of a poisonous frog?
“I can imagine that these kinds of poisons are interesting [to Russia] because they are quite difficult to detect,” says Dr Eric Franssen, doctor in clinical toxicology and pharmacology at the Department of Clinical Pharmacy, Onze Lieve Vrouwe Gasthuis hospital in the Netherlands.
Dr Franssen said: “Because in hospitals, we will not detect them in a routine toxicology screen. So perhaps this is a way to disguise intoxications.”
The UK and its allies say the toxin was derived from an Ecuadorian dart frog. These are produced naturally to ward off predators.
Sky News understands it is likely the toxin was manufactured in a laboratory rather than actually taken from the frogs. In humans, the effects are deadly.
Dr Franssen added: “We do not know very much of these toxins in humans because you cannot experiment, of course, with this kind of toxins in real life, only in animals.
“But there have been reports that people may die after 10 to 20 minutes of intake of this when you have a certain amount of these toxins.”
“This can be done by ingestion or injection in the bloodstream. I suppose then it has a direct effect on the muscles and the heart.
“And it paralyses the muscles, also your respiratory muscles. And then you become very low in your oxygen in blood. And also by cardiac failure, your brain does not receive any oxygen anymore and this may cause death.”
“Nausea and vomiting are side effects of these kinds of toxins.”
Dr Franssen’s description tallies with photos, published by Navalny’s foundation, of the prison cell where he was taken ill: vomit is clearly visible.
Read more:
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Navalny was a political dissident who challenged Putin. He survived being poisoned with the Novichok nerve agent.
When he returned to Russia in 2021, he was imprisoned and convicted on trumped-up charges.
In December 2023 Navalny was transferred from a prison outside Moscow to a penal colony in Russia’s Far North, in Kharp: the Polar Wolf colony, known for its brutal conditions, capable of holding around 1,000 prisoners.
Despite those conditions, Navalny seemed in good health – and good spirits – in a court appearance on 15 February, 2025, before his death.
Navalny died the next day.
The initial Russian explanation was that he lost consciousness after a walk.
His body was only returned to his family eight days after his death.
And the official state post mortem concluded the official cause of death was high blood pressure brought about by a chronic abnormal heart rhythm.
In September last year, Navany’s widow, Yulia Navalniya, made a dramatic revelation. She posted on social media: “In February 2024 we were able to obtain samples of Alexei’s biological material and securely smuggle them abroad. Labs in at least two countries examined these samples independently of each other and these labs in 2 diff countries reached the same conclusion Alexei was killed, more specifically he was poisoned.”
Dr Franssen said this sort of testing was feasible.
He said: “Normally, when people die, you may have autopsies, then you cool the body because you do not want that the toxins degrade in the human body after death [in order to] detect them. So it may be possible to measure toxin levels in tissue.
“That can be the lung, that can be the heart, it can be blood and urine also. But it can also be possible to detect not the native drugs but also the metabolites of these toxins. So these can stay longer in the body.”
That lab work has now been revealed by Britain and its allies.
Russian authorities insist Navalny’s death was natural.
(c) Sky News 2026: The science behind the frog poison that allegedly killed Alexei Navalny
